Enthalpy Changes in Chemical Reactions
Explore enthalpy changes, Hess's Law, and calorimetry with this Grade 12 Chemistry worksheet.
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Enthalpy Changes in Chemical Reactions
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Read each question carefully and answer to the best of your ability. Show all your work for calculations.
1. Which of the following best describes an endothermic reaction?
Releases heat to the surroundings.
Absorbs heat from the surroundings.
Has no change in heat.
Increases the temperature of the system.
2. According to Hess's Law, the total enthalpy change for a reaction is:
Dependent on the pathway taken.
The sum of the enthalpy changes for each step.
Always positive.
Always negative.
3. Enthalpy (H) is a measure of the total of a thermodynamic system.
4. A reaction with a positive ΔH is .
5. The enthalpy of formation for an element in its standard state is always zero.
True
False
6. Calorimetry is the science of measuring heat flow.
True
False
7. Explain the difference between enthalpy and internal energy.
8. Describe how a bomb calorimeter is used to determine the enthalpy of combustion.
9. Analyze the following energy diagram. Is the reaction endothermic or exothermic? Justify your answer.
10. Given the following reactions:
C(s) + O₂(g) → CO₂(g) ΔH = -393.5 kJ/mol
H₂(g) + ½O₂(g) → H₂O(l) ΔH = -285.8 kJ/mol
CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(l) ΔH = -890.3 kJ/mol
Calculate the standard enthalpy of formation of methane (CH₄(g)) using Hess's Law.