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Questions and Answers
What is the value of ΔH for the reaction between NaOH and HCl?
What is the value of ΔH for the reaction between NaOH and HCl?
- -57.3 kJ (correct)
- -176 kJ
- 0 kJ
- 57.3 kJ
What is produced from the reaction of ammonia gas with hydrogen chloride gas?
What is produced from the reaction of ammonia gas with hydrogen chloride gas?
- Hydrogen gas
- Water
- Sodium chloride
- Ammonium chloride (correct)
How is energy absorbed during a chemical reaction?
How is energy absorbed during a chemical reaction?
- When new bonds are formed
- When products are formed
- When heat is released
- When reactant bonds are broken (correct)
Which of the following indicates that a reaction is exothermic?
Which of the following indicates that a reaction is exothermic?
What type of chemical reaction occurs when ammonia and hydrogen chloride react?
What type of chemical reaction occurs when ammonia and hydrogen chloride react?
In the reaction 2H2 + O2 ⟶ 2H2O, what happens to the energy during bond making?
In the reaction 2H2 + O2 ⟶ 2H2O, what happens to the energy during bond making?
What does the negative value of ΔH (-176 kJ) for the reaction of NH3 and HCl suggest?
What does the negative value of ΔH (-176 kJ) for the reaction of NH3 and HCl suggest?
What is the role of energy in bond breaking and making during a chemical reaction?
What is the role of energy in bond breaking and making during a chemical reaction?
What happens to the temperature of the surroundings during an exothermic reaction?
What happens to the temperature of the surroundings during an exothermic reaction?
Which of the following processes is an example of an endothermic reaction?
Which of the following processes is an example of an endothermic reaction?
What does the symbol ΔH represent in thermochemistry?
What does the symbol ΔH represent in thermochemistry?
During which process is heat absorbed from the surroundings?
During which process is heat absorbed from the surroundings?
What is necessary to measure the enthalpy change in a reaction?
What is necessary to measure the enthalpy change in a reaction?
Which energy profile diagram correctly represents an endothermic reaction?
Which energy profile diagram correctly represents an endothermic reaction?
What is the main difference between exothermic and endothermic reactions?
What is the main difference between exothermic and endothermic reactions?
What is enthalpy change measured in?
What is enthalpy change measured in?
What does a negative $ ext{ΔH}$ indicate about a chemical reaction?
What does a negative $ ext{ΔH}$ indicate about a chemical reaction?
In an endothermic reaction, which of the following statements is true?
In an endothermic reaction, which of the following statements is true?
Which of the following correctly describes the energy level diagram of an exothermic reaction?
Which of the following correctly describes the energy level diagram of an exothermic reaction?
When 1 mol of NaOH reacts with 1 mol of HCl, what happens to the heat during the reaction?
When 1 mol of NaOH reacts with 1 mol of HCl, what happens to the heat during the reaction?
Which of the following is a characteristic of an energy level diagram for an endothermic reaction?
Which of the following is a characteristic of an energy level diagram for an endothermic reaction?
What does an energy level diagram typically illustrate for a chemical reaction?
What does an energy level diagram typically illustrate for a chemical reaction?
What is the sign of ΔH in an exothermic reaction?
What is the sign of ΔH in an exothermic reaction?
In the equation $ ext{NaOH (aq) + HCl (aq) ⟶ NaCl (aq) + H2O (l)}$, what does the energy change signify?
In the equation $ ext{NaOH (aq) + HCl (aq) ⟶ NaCl (aq) + H2O (l)}$, what does the energy change signify?
What does ΔH represent in a chemical reaction?
What does ΔH represent in a chemical reaction?
Which bond has the highest bond strength based on the given bond energies?
Which bond has the highest bond strength based on the given bond energies?
What is the activation energy (Ea) in a chemical reaction?
What is the activation energy (Ea) in a chemical reaction?
When reactant particles possess energy less than the activation energy, what is the expected outcome?
When reactant particles possess energy less than the activation energy, what is the expected outcome?
What is the overall ΔH for the reaction H2 (g) + Cl2 (g) ⟶ 2HCl (g)?
What is the overall ΔH for the reaction H2 (g) + Cl2 (g) ⟶ 2HCl (g)?
How are energy profile diagrams useful in understanding chemical reactions?
How are energy profile diagrams useful in understanding chemical reactions?
Which factor increases the likelihood of a chemical reaction occurring?
Which factor increases the likelihood of a chemical reaction occurring?
Who developed the Collision Theory independently?
Who developed the Collision Theory independently?
What does a negative overall enthalpy change (ΔH) indicate about a reaction?
What does a negative overall enthalpy change (ΔH) indicate about a reaction?
In the reaction 2H2 + O2 ⟶ 2H2O, what is the total energy absorbed for bond breaking?
In the reaction 2H2 + O2 ⟶ 2H2O, what is the total energy absorbed for bond breaking?
Which statement about bond energies is true?
Which statement about bond energies is true?
What calculation would you perform to determine whether a reaction is exothermic or endothermic?
What calculation would you perform to determine whether a reaction is exothermic or endothermic?
In the reaction provided, what is the bond energy of the O=O bond?
In the reaction provided, what is the bond energy of the O=O bond?
How many moles of O-H bonds are formed in the reaction of forming 2H2O?
How many moles of O-H bonds are formed in the reaction of forming 2H2O?
If the energy absorbed in bond breaking is greater than the energy released in bond making, what type of reaction is it?
If the energy absorbed in bond breaking is greater than the energy released in bond making, what type of reaction is it?
What is the total energy released upon forming 2 moles of H2O?
What is the total energy released upon forming 2 moles of H2O?
What is the significance of the principle that the energy required to break a chemical bond is equal to the energy released when the same bond is formed?
What is the significance of the principle that the energy required to break a chemical bond is equal to the energy released when the same bond is formed?
How is overall enthalpy change (ΔH) mathematically expressed?
How is overall enthalpy change (ΔH) mathematically expressed?
What is the definition of activation energy?
What is the definition of activation energy?
Which type of reaction absorbs heat from the surroundings?
Which type of reaction absorbs heat from the surroundings?
In an exothermic reaction, what happens to the energy of the products compared to the reactants?
In an exothermic reaction, what happens to the energy of the products compared to the reactants?
What occurs when ammonium nitrate is dissolved in water?
What occurs when ammonium nitrate is dissolved in water?
Which of the following correctly describes energy changes in chemical reactions?
Which of the following correctly describes energy changes in chemical reactions?
What is represented in an energy profile diagram for a chemical reaction?
What is represented in an energy profile diagram for a chemical reaction?
Which conversion between states of water is exothermic?
Which conversion between states of water is exothermic?
What kind of reaction would show an increase in temperature of the surroundings?
What kind of reaction would show an increase in temperature of the surroundings?
What does the symbol ΔH represent in a chemical reaction?
What does the symbol ΔH represent in a chemical reaction?
What happens to the temperature of the surroundings when an exothermic reaction occurs?
What happens to the temperature of the surroundings when an exothermic reaction occurs?
In a chemical reaction, if the energy absorbed in bond breaking is greater than the energy released in bond making, what type of reaction is it?
In a chemical reaction, if the energy absorbed in bond breaking is greater than the energy released in bond making, what type of reaction is it?
What is an energy profile diagram primarily used to illustrate?
What is an energy profile diagram primarily used to illustrate?
What does a negative value of ΔH indicate about a reaction?
What does a negative value of ΔH indicate about a reaction?
What does bond energy indicate about a covalent bond?
What does bond energy indicate about a covalent bond?
What is the purpose of activation energy in a chemical reaction?
What is the purpose of activation energy in a chemical reaction?
If the energy absorbed during bond breaking is 500 kJ and the energy released during bond making is 400 kJ, what type of reaction occurs?
If the energy absorbed during bond breaking is 500 kJ and the energy released during bond making is 400 kJ, what type of reaction occurs?
Which of the following statements about collision theory is accurate?
Which of the following statements about collision theory is accurate?
Which bond has the highest bond energy based on the provided values?
Which bond has the highest bond energy based on the provided values?
What does the overall ΔH of -184 kJ for the reaction H2 (g) + Cl2 (g) ⟶ 2HCl (g) indicate?
What does the overall ΔH of -184 kJ for the reaction H2 (g) + Cl2 (g) ⟶ 2HCl (g) indicate?
How is an energy profile diagram useful in the study of chemical reactions?
How is an energy profile diagram useful in the study of chemical reactions?
Which of the following correctly describes the relationship between bond strength and bond energy?
Which of the following correctly describes the relationship between bond strength and bond energy?
What is the sign of ΔH for the reaction between ammonia gas and hydrogen chloride gas?
What is the sign of ΔH for the reaction between ammonia gas and hydrogen chloride gas?
What occurs when bonds are formed during a chemical reaction?
What occurs when bonds are formed during a chemical reaction?
In the reaction 2H2 + O2 ⟶ 2H2O, what is the general trend regarding energy changes?
In the reaction 2H2 + O2 ⟶ 2H2O, what is the general trend regarding energy changes?
Which of the following statements is true regarding an exothermic reaction?
Which of the following statements is true regarding an exothermic reaction?
Which process is associated with a negative ΔH value?
Which process is associated with a negative ΔH value?
What is the common characteristic of exothermic reactions in terms of temperature?
What is the common characteristic of exothermic reactions in terms of temperature?
Which type of energy change occurs during the breaking of bonds?
Which type of energy change occurs during the breaking of bonds?
What is indicated by the reaction ΔH = -57.3 kJ for reactants NaOH and HCl?
What is indicated by the reaction ΔH = -57.3 kJ for reactants NaOH and HCl?
What happens when the energy absorbed for bond breaking is equal to the energy released for bond making?
What happens when the energy absorbed for bond breaking is equal to the energy released for bond making?
How is overall enthalpy change (ΔH) calculated for a chemical reaction?
How is overall enthalpy change (ΔH) calculated for a chemical reaction?
If a reaction has an overall enthalpy change (ΔH) of -484 kJ, what type of reaction is it?
If a reaction has an overall enthalpy change (ΔH) of -484 kJ, what type of reaction is it?
What is the significance of the principle that energy required to break a bond is equal to the energy released when the bond is formed?
What is the significance of the principle that energy required to break a bond is equal to the energy released when the bond is formed?
Which of the following correctly describes the energy dynamics in the reaction of H2 and O2 forming H2O?
Which of the following correctly describes the energy dynamics in the reaction of H2 and O2 forming H2O?
What would likely occur if the energy absorbed in bond breaking is less than the energy released in bond making?
What would likely occur if the energy absorbed in bond breaking is less than the energy released in bond making?
Which of the following is an example of energy being released during bond formation?
Which of the following is an example of energy being released during bond formation?
What is the primary effect of activation energy on a chemical reaction?
What is the primary effect of activation energy on a chemical reaction?
Which statement accurately describes an endothermic reaction?
Which statement accurately describes an endothermic reaction?
In an energy profile diagram, what does the area between the reactants and the transition state represent?
In an energy profile diagram, what does the area between the reactants and the transition state represent?
When ammonium nitrate dissolves in water and the water temperature drops, which type of reaction is occurring?
When ammonium nitrate dissolves in water and the water temperature drops, which type of reaction is occurring?
How is the overall enthalpy change (ΔH) for a chemical reaction calculated?
How is the overall enthalpy change (ΔH) for a chemical reaction calculated?
Which statement is true regarding the total energy of products in an endothermic reaction?
Which statement is true regarding the total energy of products in an endothermic reaction?
How is an exothermic reaction characterized in terms of heat exchange?
How is an exothermic reaction characterized in terms of heat exchange?
What does a positive ΔH value indicate about a chemical reaction?
What does a positive ΔH value indicate about a chemical reaction?
In an energy level diagram for a reaction, what does the height of the reactants represent?
In an energy level diagram for a reaction, what does the height of the reactants represent?
Which of the following best describes the heat of reaction (ΔH) for the reaction NaOH + HCl?
Which of the following best describes the heat of reaction (ΔH) for the reaction NaOH + HCl?
Which energy change occurs when the bonds in the products of an endothermic reaction are formed?
Which energy change occurs when the bonds in the products of an endothermic reaction are formed?
What happens to the surroundings during an exothermic chemical reaction?
What happens to the surroundings during an exothermic chemical reaction?
Flashcards
Exothermic reaction
Exothermic reaction
A reaction that releases heat to the surroundings.
Endothermic reaction
Endothermic reaction
A reaction that absorbs heat from the surroundings.
Enthalpy change
Enthalpy change
The amount of energy involved in a reaction.
ΔH
ΔH
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Energy change
Energy change
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Combustion
Combustion
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Melting
Melting
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Bond forming
Bond forming
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ΔH (negative)
ΔH (negative)
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ΔH (positive)
ΔH (positive)
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Energy Level Diagram
Energy Level Diagram
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Total energy of products
Total energy of products
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Total energy of reactants
Total energy of reactants
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Bond Breaking
Bond Breaking
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Bond Making
Bond Making
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Energy Change in Reactions
Energy Change in Reactions
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Negative ΔH
Negative ΔH
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Ammonia and Hydrogen Chloride Reaction
Ammonia and Hydrogen Chloride Reaction
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Enthalpy Change (ΔH)
Enthalpy Change (ΔH)
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Energy Absorbed for Bond Breaking
Energy Absorbed for Bond Breaking
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Energy Released for Bond Making
Energy Released for Bond Making
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Relating Bond Energy to ΔH
Relating Bond Energy to ΔH
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Bond Energy
Bond Energy
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Calculating ΔH
Calculating ΔH
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Bond Strength
Bond Strength
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Activation Energy (Ea)
Activation Energy (Ea)
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Collision Theory
Collision Theory
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Energy Profile Diagram
Energy Profile Diagram
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Reactants have less energy than Ea
Reactants have less energy than Ea
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Reactants have enough energy for Ea
Reactants have enough energy for Ea
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Overall ΔH for a reaction
Overall ΔH for a reaction
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Activation Energy
Activation Energy
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What does a negative ΔH value indicate?
What does a negative ΔH value indicate?
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What does a positive ΔH value indicate?
What does a positive ΔH value indicate?
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What is the relationship between ΔH and the energy profile diagram?
What is the relationship between ΔH and the energy profile diagram?
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ΔH (enthalpy change)
ΔH (enthalpy change)
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What does a negative ΔH indicate?
What does a negative ΔH indicate?
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NaOH + HCl reaction
NaOH + HCl reaction
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What does a positive ΔH indicate?
What does a positive ΔH indicate?
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Energy level diagram for exothermic reaction
Energy level diagram for exothermic reaction
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ΔH value
ΔH value
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How is ΔH related to bond breaking and making?
How is ΔH related to bond breaking and making?
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What is bond energy?
What is bond energy?
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How do we calculate ΔH?
How do we calculate ΔH?
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What is ΔH?
What is ΔH?
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What does a negative ΔH indicate on an Energy Profile Diagram?
What does a negative ΔH indicate on an Energy Profile Diagram?
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Overall Enthalpy Change
Overall Enthalpy Change
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Study Notes
Thermochemistry Overview
- Thermochemistry is the study of energy changes in chemical reactions.
- Energy cannot be created or destroyed, only changed from one form to another.
- All chemical reactions involve energy changes.
- Some physical changes also involve energy changes.
- Energy changes can be observed as changes in temperature.
Learning Objectives
- Describe enthalpy change in terms of exothermic and endothermic changes.
- Draw energy level diagrams.
- Explain bond breaking (endothermic) and bond forming (exothermic) processes.
- Explain overall enthalpy changes in terms of energy changes associated with breaking and making covalent bonds.
- Draw energy profile diagrams to represent exothermic and endothermic reactions and show activation energies.
Exothermic & Endothermic Reactions
- Exothermic: Heat is given off to the surroundings; surrounding temperature rises.
- Examples: combustion of fuels, dissolving acids, condensation, freezing.
- Endothermic: Heat is absorbed from the surroundings; surrounding temperature drops.
- Examples: dissolving some ionic compounds in water, evaporation, melting.
Enthalpy Change in a Reaction
- Enthalpy change (ΔH) is the amount of energy involved in a reaction.
- Measured in kilojoules (kJ).
- Represented by the symbol ΔH.
- ΔH = total energy of products – total energy of reactants
Energy Level Diagrams
- Show energy changes in reactions.
- Exothermic reactions: Products have lower energy than reactants; ΔH is negative. The amount of energy released, is the magnitude of ΔH.
- Endothermic reactions: Products have higher energy than reactants; ΔH is positive. The amount of energy absorbed, is the magnitude of ΔH
Bond Breaking & Bond Making
- Energy is required to break bonds (endothermic).
- Energy is released when bonds are formed (exothermic).
- The overall enthalpy change depends on the difference between energy absorbed for breaking bonds and energy released for making bonds.
- Bond energy is the energy required to break one mole of a specific bond.
Activation Energy
- Activation energy (Ea) is the minimum energy needed for a chemical reaction to occur.
- Reactant particles need to possess this minimum energy for a reaction to start.
- Represents a barrier in the reaction process.
- Activation energy is shown on energy profile diagrams.
Collision Theory
- Developed independently by Max Trautz and William Lewis (in 1916 and 1918 respectively).
- Explains how reactant particles need to collide in proper orientation with enough energy to cause a reaction.
Energy Profile Diagrams
- Illustrate the energy changes during a reaction.
- Show the enthalpy change (ΔH) and activation energy (Ea).
- Exothermic reactions have products with lower energy than reactants, Ea is needed in the reaction to achieve the products.
- Endothermic reactions have products with higher energy than reactants, Ea is needed in the reaction to achieve the products.
Practice Questions & Examples
- Specific examples of calculations and explanations provided for different chemical reactions such as NaOH and HCl reaction, Haber process, and reaction of Hydrogen gas and oxygen.
- Include calculations for determining overall enthalpy change.
Additional Concepts
- Water exists in solid, liquid, and gas states depending on environmental conditions.
- Exothermic conversions between these states are relevant for thermochemistry questions.
- Examples of exothermic conversions between the three states of water include freezing and condensation.
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Description
This quiz covers the fundamental principles of thermochemistry, including energy changes in chemical reactions, enthalpy changes, and differentiating between exothermic and endothermic processes. Test your knowledge on energy level diagrams and activation energies through various questions related to the energy transformations in chemical reactions.
