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Questions and Answers
In an exothermic reaction, what best describes the energy level of the products compared to the reactants?
In an exothermic reaction, what best describes the energy level of the products compared to the reactants?
- The products have higher energy than the reactants.
- The products and reactants have the same energy level.
- The products have lower energy than the reactants. (correct)
- There is no overall change in energy involved in the reaction.
Which of the following is a characteristic of an endothermic reaction?
Which of the following is a characteristic of an endothermic reaction?
- Releases heat into the surrounding environment.
- Results in a net decrease in energy.
- Forms products with lower energy than the reactants.
- Absorbs heat from the surrounding environment. (correct)
Which of the following processes describes the breaking of bonds?
Which of the following processes describes the breaking of bonds?
- Endothermic, because heat is released into the surroundings.
- Exothermic, because heat is absorbed from the surroundings.
- Endothermic, because energy is required to break bonds. (correct)
- Exothermic, because energy is released as bonds break.
Which of the following best describes the role of energy in bond formation?
Which of the following best describes the role of energy in bond formation?
Which of the following processes represents an exothermic reaction?
Which of the following processes represents an exothermic reaction?
If a reaction involves breaking 2 moles of C-H bonds and forming 1 mole of O=O bonds, how would you classify the energy change associated with these specific bond changes?
If a reaction involves breaking 2 moles of C-H bonds and forming 1 mole of O=O bonds, how would you classify the energy change associated with these specific bond changes?
Which statement accurately uses bond energy to explain why some reactions are exothermic?
Which statement accurately uses bond energy to explain why some reactions are exothermic?
Flashcards
Exothermic Reaction
Exothermic Reaction
A reaction that releases energy, products have lower energy than the reactants.
Endothermic Reaction
Endothermic Reaction
A reaction that absorbs energy; products have higher energy than reactants.
Energy Changes in Reactions
Energy Changes in Reactions
A type of chemical reaction that always involves an energy change, usually in the form of heat.
Breaking Bonds (Endothermic)
Breaking Bonds (Endothermic)
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Making Bonds (Exothermic)
Making Bonds (Exothermic)
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Examples of Exothermic Reactions
Examples of Exothermic Reactions
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Examples of Endothermic Reactions
Examples of Endothermic Reactions
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Study Notes
- Chemical Energetics involves the study of energy changes in reactions.
- Energy is either absorbed or released during a chemical reaction, usually in the form of heat.
- Reactions are classified into exothermic and endothermic based on energy transfer
Exothermic Reactions
- Reactions can be described with reactants yielding products, and energy being released
- Reactants ----> products + energy
- The total energy remains constant throughout the reaction.
- Products have less energy than reactants in exothermic reactions.
- Heat is released
- ΔH (change in enthalpy) is negative
Endothermic Reactions
- Reactions can be described with reactants plus energy yielding products
- reactants + energy-----> products
- The total energy is the same on each side of the arrow, in a reaction
- The products have higher energy than reactants, since energy is absorbed.
- ΔH (change in enthalpy) is positive
Examples of Reactions
- Exothermic reactions include rusting iron, condensation of rain, formation of snow in clouds, making ice cubes, and burning sugar.
- Endothermic reactions include cooking an egg, evaporation of water, conversion of frost to water vapor, melting ice cubes, and producing sugar by photosynthesis.
Explaining Energy Changes
- Bonds must be broken first to start a chemical reaction
- Then new bonds form.
- Breaking bonds requires the absorption of energy, making it is an endothermic process.
- Making bonds releases energy, which is an exothermic process.
Bond Energy
- Bond breaking is endothermic, requiring energy input.
- Example: C-H + energy → C H
- Bond formation is exothermic, releasing energy.
- Example: H H → H-H + energy
- A greater bond energy indicates a stronger bond.
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