Exothermic and Endothermic Reactions
Subject :Chemistry
Term : Second Term
Week :Week 2
Topic : Exothermic and Endothermic Reactions
Behavioural Objectives :By the end of the lesson, students should be able to
- understand the basic principles of thermodynamics
- explain the concept of heat of reaction, as well as the laws of thermodynamics that govern them.
Materials Needed :
- Whiteboard or blackboard
- Markers or chalk
- Handouts on thermodynamics and heat of reaction
- Visual aids (e.g., diagrams, charts)
- PowerPoint presentation
- Handouts with practice problems
- Chemicals and apparatus for demonstration experiments (optional)
Content
Exothermic and Endothermic Reactions
Chemical reactions can be classified based on the energy changes that occur during the reaction. Two common types of energy changes are exothermic and endothermic reactions.
- Exothermic reactions: An exothermic reaction releases energy in the form of heat. In these reactions, the products have less energy than the reactants. This energy difference is released as heat and usually makes the reaction feel hot.
Example: Combustion of wood: The combustion of wood is an example of an exothermic reaction. When wood burns, it reacts with oxygen to form carbon dioxide and water. The energy that is released during this reaction is given off as heat and light.
C6H12O6 + 6O2 → 6CO2 + 6H2O + energy
- Endothermic reactions: An endothermic reaction absorbs energy in the form of heat. In these reactions, the products have more energy than the reactants. This energy difference is absorbed from the surroundings, and usually makes the reaction feel cold.
Example: Dissolving ammonium nitrate in water: The dissolving of ammonium nitrate in water is an example of an endothermic reaction. When ammonium nitrate dissolves in water, it absorbs heat from the surroundings, making the water feel cold.
NH4NO3 + H2O → NH4+ + NO3- + energy
In conclusion, exothermic reactions release energy in the form of heat while endothermic reactions absorb energy in the form of heat. These energy changes are important to understand because they can have practical applications in many fields, including chemistry, physics, and engineering.
Evaluation
- Which of the following statements describes an exothermic reaction? a) Energy is absorbed from the surroundings. b) Energy is released to the surroundings. c) The products have more energy than the reactants. d) The reaction feels cold.
Answer: b) Energy is released to the surroundings.
- What happens to the energy during an endothermic reaction? a) It is released to the surroundings. b) It is absorbed from the surroundings. c) It remains constant. d) It is converted to light.
Answer: b) It is absorbed from the surroundings.
- Which of the following is an example of an exothermic reaction? a) The melting of ice. b) The evaporation of water. c) The combustion of methane. d) The dissolution of sugar in water.
Answer: c) The combustion of methane.
- When ammonium chloride is dissolved in water, the solution feels cold. This is an example of a(n) _____ reaction. a) endothermic b) exothermic c) neutral d) reversible
Answer: a) endothermic
- In an exothermic reaction, the energy of the products is _____ the energy of the reactants. a) greater than b) less than c) equal to d) unrelated to
Answer: b) less than
- Which of the following reactions is endothermic? a) NaOH + HCl → NaCl + H2O b) 2H2 + O2 → 2H2O c) NH4NO3 → N2O + 2H2O d) Fe + Cl2 → FeCl3
Answer: c) NH4NO3 → N2O + 2H2O
- Which of the following is an example of an endothermic reaction that occurs in the human body? a) Digestion of food. b) Synthesis of proteins. c) Muscle contraction. d) Sweating.
Answer: b) Synthesis of proteins.
- Which of the following factors can increase the rate of an exothermic reaction? a) Decreasing the temperature. b) Decreasing the concentration of reactants. c) Increasing the surface area of reactants. d) Adding a catalyst.
Answer: c) Increasing the surface area of reactants.
- Which of the following is an example of a reaction that is both exothermic and reversible? a) The formation of water from hydrogen and oxygen. b) The combustion of methane. c) The conversion of graphite to diamond. d) The dissociation of ammonium chloride in water.
Answer: a) The formation of water from hydrogen and oxygen.
- When a reaction is endothermic, the value of ΔH is _____. a) positive b) negative c) zero d) cannot be determined
Answer: a) positive.
HEAT OF REACTION AND CHEMICAL BONDS
During chemical reactions, chemical bonds are broken, atoms are regrouped and new bonds are formed.
Bond breaking requires energy and bond forming evolves energy. The minimum amount of energy required for bond breaking is called activation energy. While bond breaking is endothermic, bond forming is exothermic.
Thus, heat of reaction comes from breaking and forming of chemicals bond. Heat reaction is negative [exothermic] when bond-breaking energy is less than bond forming energy.
Heat of reaction is positive [endothermic] when bond-breaking energy is more than bond forming energy.
Chemical reactions involve breaking and forming of chemical bonds. Chemical bonds are the attractive forces that hold atoms together to form molecules. During chemical reactions, some bonds are broken and new bonds are formed. This process requires or releases energy, which is measured as the heat of reaction. The heat of reaction is the amount of heat energy that is either absorbed or released during a chemical reaction.
The heat of reaction can be classified as either exothermic or endothermic depending on the net energy change in the system. Exothermic reactions release energy into the surroundings, while endothermic reactions absorb energy from the surroundings.
For example, the combustion of methane gas is an exothermic reaction. During this reaction, the carbon-hydrogen bonds in methane are broken and new bonds are formed with oxygen to produce carbon dioxide and water. The energy released during this process is given off as heat and light.
CH4 + 2O2 → CO2 + 2H2O + heat
On the other hand, the reaction of baking soda and vinegar is an endothermic reaction. During this reaction, the bonds in baking soda (sodium bicarbonate) and vinegar (acetic acid) are broken, and new bonds are formed to produce carbon dioxide gas, water, and sodium acetate. The reaction absorbs energy from the surroundings, causing the reaction to feel cold.
NaHCO3 + CH3COOH → CO2 + H2O + NaC2H3O2 + heat
In conclusion, the heat of reaction is determined by the difference between the bond breaking and bond forming energies in a chemical reaction. The heat of reaction can be used to predict the direction and extent of a chemical reaction, and it is an important concept in the field of thermodynamics
HEAT OF REACTION AND CHEMICAL BONDS
During chemical reactions, chemical bonds are broken, atoms are regrouped and new bonds are formed. Bond breaking requires energy and bond forming evolves energy. The minimum amount of energy required for bond breaking is called activation energy. While bond breaking is endothermic, bond forming is exothermic. Thus, heat of reaction comes from breaking and forming of chemicals bond. Heat reaction is negative [exothermic] when bond-breaking energy is less than bond forming energy. Heat of reaction is positive [endothermic] when bond-breaking energy is more than bond forming energy.
Evaluation
- What is activation energy? a) The energy required for bond forming b) The energy required for bond breaking c) The energy released during a chemical reaction d) The energy absorbed during a chemical reaction
Answer: b) The energy required for bond breaking
- What is the heat of reaction? a) The energy required to start a chemical reaction b) The energy released during a chemical reaction c) The energy absorbed during a chemical reaction d) The energy required to break chemical bonds
Answer: b) The energy released during a chemical reaction
- What is an exothermic reaction? a) A reaction that absorbs energy from the surroundings b) A reaction that releases energy to the surroundings c) A reaction that does not involve any energy change d) A reaction that produces light but no heat
Answer: b) A reaction that releases energy to the surroundings
- What is an endothermic reaction? a) A reaction that absorbs energy from the surroundings b) A reaction that releases energy to the surroundings c) A reaction that does not involve any energy change d) A reaction that produces light but no heat
Answer: a) A reaction that absorbs energy from the surroundings
- What is the relationship between bond breaking and energy? a) Bond breaking releases energy b) Bond breaking absorbs energy c) Bond forming releases energy d) Bond forming absorbs energy
Answer: b) Bond breaking absorbs energy
- Which of the following is an example of an exothermic reaction? a) Photosynthesis b) Electrolysis of water c) Respiration d) Combustion of gasoline
Answer: d) Combustion of gasoline
- Which of the following is an example of an endothermic reaction? a) Rusting of iron b) Burning of magnesium c) Dissolving of ammonium nitrate in water d) Neutralization of hydrochloric acid with sodium hydroxide
Answer: c) Dissolving of ammonium nitrate in water
- What is the heat of reaction for an exothermic reaction? a) Positive b) Negative c) Zero d) Undefined
Answer: b) Negative
- What is the heat of reaction for an endothermic reaction? a) Positive b) Negative c) Zero d) Undefined
Answer: a) Positive
- What is the minimum amount of energy required for bond breaking? a) Heat of reaction b) Bond forming energy c) Activation energy d) Bond breaking energy
Answer: c) Activation energy
Heat of combustion:
The heat of combustion is the amount of heat energy released when one mole of a substance undergoes complete combustion with oxygen. During combustion, the substance reacts with oxygen to produce carbon dioxide and water, and the energy released during this process is given off as heat.
For example, the heat of combustion of methane gas (CH4) is -890 kJ/mol. This means that when one mole of methane gas reacts with oxygen to form carbon dioxide and water, 890 kJ of heat energy is released.
CH4 + 2O2 → CO2 + 2H2O + heat
The heat of combustion is an important concept in the field of energy because it is used to determine the energy content of fuels. The higher the heat of combustion of a fuel, the more energy it can release when burned.
Heat of neutralization:
The heat of neutralization is the amount of heat energy released or absorbed when an acid and a base react to form a salt and water. In neutralization reactions, the acid donates a proton (H+) to the base, forming a salt and water. The energy released or absorbed during this process is given off as heat.
For example, the heat of neutralization of hydrochloric acid (HCl) and sodium hydroxide (NaOH) is -57.1 kJ/mol. This means that when one mole of hydrochloric acid reacts with one mole of sodium hydroxide, 57.1 kJ of heat energy is released.
HCl + NaOH → NaCl + H2O + heat
The heat of neutralization is an important concept in the field of chemistry because it can be used to determine the strength of acids and bases. Stronger acids and bases release more heat during neutralization reactions than weaker acids and bases.
In conclusion, the heat of combustion and the heat of neutralization are important concepts in the field of chemistry. The heat of combustion is used to determine the energy content of fuels, while the heat of neutralization is used to determine the strength of acids and bases
Evaluation
- What is the heat of combustion? a) The amount of heat energy absorbed when a substance is burned. b) The amount of heat energy released when a substance is burned. c) The amount of heat energy absorbed during a chemical reaction. d) The amount of heat energy released during a chemical reaction.
Answer: b) The amount of heat energy released when a substance is burned.
- What is the heat of neutralization? a) The amount of heat energy absorbed when an acid and a base react. b) The amount of heat energy released when an acid and a base react. c) The amount of heat energy absorbed when a substance is burned. d) The amount of heat energy released when a substance is burned.
Answer: b) The amount of heat energy released when an acid and a base react.
- Which of the following is an example of a neutralization reaction? a) Burning of methane gas b) Reaction of sodium metal with water c) Reaction of hydrochloric acid with sodium hydroxide d) Reaction of magnesium metal with hydrochloric acid
Answer: c) Reaction of hydrochloric acid with sodium hydroxide
- What is the heat of combustion of methane gas? a) -890 kJ/mol b) +890 kJ/mol c) -57.1 kJ/mol d) +57.1 kJ/mol
Answer: a) -890 kJ/mol
- Which of the following is an exothermic process? a) Combustion of gasoline b) Melting of ice c) Dissolving of salt in water d) Evaporation of water
Answer: a) Combustion of gasoline
- What is the product of a neutralization reaction? a) Salt and water b) Carbon dioxide and water c) Oxygen and water d) Hydrogen gas and oxygen gas
Answer: a) Salt and water
- Which of the following is an example of a strong acid? a) Acetic acid b) Hydrochloric acid c) Citric acid d) Carbonic acid
Answer: b) Hydrochloric acid
- What is the heat of neutralization for the reaction between sulfuric acid (H2SO4) and sodium hydroxide (NaOH)? a) -57.1 kJ/mol b) -192.5 kJ/mol c) -1414 kJ/mol d) +1414 kJ/mol
Answer: b) -192.5 kJ/mol
- What is the heat of combustion used for? a) To determine the strength of acids and bases b) To determine the energy content of fuels c) To determine the pH of a solution d) To determine the concentration of a solution
Answer: b) To determine the energy content of fuels
- Which of the following is an example of an endothermic process? a) Formation of ice from water b) Combustion of gasoline c) Dissolving of sodium chloride in water d) Neutralization of hydrochloric acid with sodium hydroxide
Answer: a) Formation of ice from water
THERMODYNAMICS
Thermodynamics is a branch of physics that deals with the study of heat and temperature, and their relation to energy and work. It is concerned with the way energy is converted from one form to another and how it affects the physical properties of matter.
There are three main laws of thermodynamics:
- The first law of thermodynamics, also known as the law of conservation of energy, states that energy cannot be created or destroyed, only transferred or converted from one form to another. This means that the total energy in a closed system remains constant.
- The second law of thermodynamics states that the total entropy (or disorder) of a closed system always increases over time. This means that all natural processes tend to move towards a state of greater disorder.
- The third law of thermodynamics states that it is impossible to reach absolute zero temperature, where all molecular motion ceases.
Thermodynamics is used in various fields such as engineering, chemistry, biology, and meteorology. Some applications of thermodynamics include the design of engines, refrigeration systems, and power plants.
Overall, thermodynamics provides a fundamental understanding of the behavior of matter and energy, and it has important practical applications in a wide range of fields
Evaluation
- Which law of thermodynamics states that energy cannot be created or destroyed, only transferred or converted from one form to another? a) First law of thermodynamics b) Second law of thermodynamics c) Third law of thermodynamics d) Zeroth law of thermodynamics
Answer: a) First law of thermodynamics
- Which law of thermodynamics states that the total entropy of a closed system always increases over time? a) First law of thermodynamics b) Second law of thermodynamics c) Third law of thermodynamics d) Zeroth law of thermodynamics
Answer: b) Second law of thermodynamics
- Which law of thermodynamics states that it is impossible to reach absolute zero temperature? a) First law of thermodynamics b) Second law of thermodynamics c) Third law of thermodynamics d) Zeroth law of thermodynamics
Answer: c) Third law of thermodynamics
- Which law of thermodynamics deals with thermal equilibrium between systems? a) First law of thermodynamics b) Second law of thermodynamics c) Third law of thermodynamics d) Zeroth law of thermodynamics
Answer: d) Zeroth law of thermodynamics
- The first law of thermodynamics is also known as: a) The law of thermal equilibrium b) The law of conservation of energy c) The law of increasing entropy d) The law of absolute zero
Answer: b) The law of conservation of energy
- Which law of thermodynamics deals with the direction of natural processes? a) First law of thermodynamics b) Second law of thermodynamics c) Third law of thermodynamics d) Zeroth law of thermodynamics
Answer: b) Second law of thermodynamics
- The second law of thermodynamics predicts that all natural processes tend to move towards a state of: a) Lower temperature b) Higher temperature c) Lower entropy d) Greater entropy
Answer: d) Greater entropy
- Which law of thermodynamics is concerned with the impossibility of reaching absolute zero temperature? a) First law of thermodynamics b) Second law of thermodynamics c) Third law of thermodynamics d) Zeroth law of thermodynamics
Answer: c) Third law of thermodynamics
- Which law of thermodynamics is concerned with the conservation of energy? a) First law of thermodynamics b) Second law of thermodynamics c) Third law of thermodynamics d) Zeroth law of thermodynamics
Answer: a) First law of thermodynamics
- Which law of thermodynamics is concerned with the thermal equilibrium between systems? a) First law of thermodynamics b) Second law of thermodynamics c) Third law of thermodynamics d) Zeroth law of thermodynamics
Answer: d) Zeroth law of thermodynamics
Evaluation
- The study of heat and temperature and their relation to energy and work is known as ________________.
Answer: Thermodynamics
- The first law of thermodynamics states that energy cannot be ___________________.
Answer: created or destroyed
- The second law of thermodynamics states that the total entropy of a closed system always ________________ over time.
Answer: increases
- The third law of thermodynamics states that it is impossible to reach ________________ temperature.
Answer: absolute zero
- Thermodynamics is used in various fields such as ________________, chemistry, biology, and meteorology.
Answer: engineering
- The heat of combustion is the amount of heat energy released when one mole of a substance undergoes ________________.
Answer: complete combustion with oxygen
- The heat of neutralization is the amount of heat energy released or absorbed when an acid and a base react to form a salt and ________________.
Answer: water
- Bond breaking is an ________________ process.
Answer: endothermic
- The minimum amount of energy required for bond breaking is called ________________.
Answer: activation energy
- The higher the heat of combustion of a fuel, the more energy it can release when ________________.
Answer: burned
Classwork
- Which branch of physics deals with the study of heat and temperature? a) Mechanics b) Optics c) Thermodynamics d) Electromagnetism
Answer: c) Thermodynamics
- Which law of thermodynamics states that energy cannot be created or destroyed, only transferred or converted from one form to another? a) First law of thermodynamics b) Second law of thermodynamics c) Third law of thermodynamics d) Zeroth law of thermodynamics
Answer: a) First law of thermodynamics
- What does the second law of thermodynamics predict? a) All natural processes tend to move towards a state of greater order. b) The total energy in a closed system remains constant. c) Energy cannot be converted from one form to another. d) All natural processes tend to move towards a state of greater disorder.
Answer: d) All natural processes tend to move towards a state of greater disorder.
- What does the third law of thermodynamics state? a) The total energy in a closed system remains constant. b) Energy cannot be created or destroyed, only transferred or converted from one form to another. c) All natural processes tend to move towards a state of greater disorder. d) It is impossible to reach absolute zero temperature.
Answer: d) It is impossible to reach absolute zero temperature.
- What is the heat of combustion? a) The amount of heat energy absorbed during a chemical reaction. b) The amount of heat energy released during a chemical reaction. c) The amount of heat energy absorbed when an acid and a base react. d) The amount of heat energy released when an acid and a base react.
Answer: b) The amount of heat energy released during a chemical reaction
- Which law of thermodynamics is concerned with thermal equilibrium between systems? a) First law of thermodynamics b) Second law of thermodynamics c) Third law of thermodynamics d) Zeroth law of thermodynamics
Answer: d) Zeroth law of thermodynamics
- What is the heat of neutralization? a) The amount of heat energy absorbed when an acid and a base react. b) The amount of heat energy released when an acid and a base react. c) The amount of heat energy absorbed during a chemical reaction. d) The amount of heat energy released during a chemical reaction.
Answer: b) The amount of heat energy released when an acid and a base react.
- What is the relationship between bond breaking and energy? a) Bond breaking releases energy. b) Bond breaking absorbs energy. c) Bond forming releases energy. d) Bond forming absorbs energy.
Answer: b) Bond breaking absorbs energy.
- Which law of thermodynamics is concerned with the direction of natural processes? a) First law of thermodynamics b) Second law of thermodynamics c) Third law of thermodynamics d) Zeroth law of thermodynamics
Answer: b) Second law of thermodynamics
- What is the minimum amount of energy required for bond breaking? a) Heat of reaction b) Bond forming energy c) Activation energy d) Bond breaking energy
Answer: c) Activation energy
Lesson Presentation
Procedure:
I. Introduction (5 minutes)
- Greet the students and introduce the topic of thermodynamics and heat of reaction.
- Explain the objectives of the lesson and the relevance of the topic to the students.
II. Presentation (30 minutes)
- Define thermodynamics and its basic principles.
- Explain the three laws of thermodynamics and their applications.
- Introduce the concept of heat of reaction and its relation to chemical bonds.
- Provide examples of exothermic and endothermic reactions.
- Discuss the difference between heat of combustion and heat of neutralization.
- Use visual aids and diagrams to illustrate the concepts.
III. Group Activity (15 minutes)
- Divide the students into small groups.
- Provide them with handouts on thermodynamics and heat of reaction.
- Ask them to discuss and solve problems related to the topic.
- Encourage them to ask questions and seek clarification.
IV. Recap (10 minutes)
- Recap the main points of the lesson.
- Ask the students to share their thoughts and feedback.
- Provide additional resources for further learning.
Assessment:
- Evaluate the students’ understanding of the topic through their participation in the group activity and their ability to answer questions related to the lesson.
- Provide feedback and suggestions for improvement.
Conclusion:
- Summarize the key takeaways from the lesson.
- Encourage the students to continue exploring the topic and its applications in various fields
Weekly Assessment /Test
- What is thermodynamics? a) The study of heat and temperature b) The study of plants and animals c) The study of rocks and minerals
Answer: a) The study of heat and temperature
- What is the first law of thermodynamics? a) Energy cannot be created or destroyed b) The total entropy of a closed system always increases c) It is impossible to reach absolute zero temperature
Answer: a) Energy cannot be created or destroyed
- What is the second law of thermodynamics? a) Energy cannot be created or destroyed b) The total entropy of a closed system always increases c) It is impossible to reach absolute zero temperature
Answer: b) The total entropy of a closed system always increases
- What is the third law of thermodynamics? a) Energy cannot be created or destroyed b) The total entropy of a closed system always increases c) It is impossible to reach absolute zero temperature
Answer: c) It is impossible to reach absolute zero temperature
- What is the heat of combustion? a) The amount of heat energy absorbed during a chemical reaction b) The amount of heat energy released during a chemical reaction c) The amount of heat energy absorbed when an acid and a base react
Answer: b) The amount of heat energy released during a chemical reaction
- What is the heat of neutralization? a) The amount of heat energy absorbed when an acid and a base react b) The amount of heat energy released when an acid and a base react c) The amount of heat energy absorbed during a chemical reaction
Answer: b) The amount of heat energy released when an acid and a base react
- What is activation energy? a) The minimum amount of energy required for bond breaking b) The maximum amount of energy required for bond forming c) The amount of energy released during a chemical reaction
Answer: a) The minimum amount of energy required for bond breaking
- What is an exothermic reaction? a) A reaction that releases heat energy b) A reaction that absorbs heat energy c) A reaction that does not involve heat energy
Answer: a) A reaction that releases heat energy
- What is an endothermic reaction? a) A reaction that releases heat energy b) A reaction that absorbs heat energy c) A reaction that does not involve heat energy
Answer: b) A reaction that absorbs heat energy
- What are the three laws of thermodynamics? a) The laws of energy, mass, and motion b) The laws of temperature, pressure, and volume c) The laws of conservation of energy, increasing entropy, and absolute zero
Answer: c) The laws of conservation of energy, increasing entropy, and absolute zero
