Enthalpy Stoichiometry Worksheet
Explore enthalpy changes in chemical reactions, calculate heats of reaction, and apply stoichiometric principles to thermochemistry.
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Enthalpy Stoichiometry
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Read each question carefully and provide detailed answers. Show all your work for calculation problems.
1. Which of the following best describes an exothermic reaction?
A reaction that absorbs heat from its surroundings.
A reaction that releases heat to its surroundings.
A reaction that has no change in temperature.
A reaction that requires light to proceed.
2. What is the standard enthalpy of formation (ΔH°f) for an element in its most stable form?
Always positive
Always negative
Zero
Depends on the element
3. The heat absorbed or released in a chemical reaction at constant pressure is called the .
4. Hess's Law states that if a reaction can be expressed as the sum of two or more steps, the enthalpy change for the overall reaction is the of the enthalpy changes for the individual steps.
5. Consider the following reaction: 2H₂(g) + O₂(g) → 2H₂O(l) ΔH = -571.6 kJ. Is this reaction endothermic or exothermic? Justify your answer.
6. Calculate the enthalpy change (ΔH) for the following reaction using the given standard enthalpies of formation (ΔH°f): C₃H₈(g) + 5O₂(g) → 3CO₂(g) + 4H₂O(l) Given: ΔH°f [C₃H₈(g)] = -103.8 kJ/mol ΔH°f [CO₂(g)] = -393.5 kJ/mol ΔH°f [H₂O(l)] = -285.8 kJ/mol ΔH°f [O₂(g)] = 0 kJ/mol
7. Energy is neither created nor destroyed in a chemical reaction.
True
False
8. A positive enthalpy change (ΔH) indicates an exothermic reaction.
True
False
Match the term with its definition.
9. Enthalpy
a. Energy required to break a bond
10. Endothermic
b. Heat content of a system at constant pressure
11. Bond energy
c. Reaction that absorbs heat