Heat of Formation Worksheet
Grade 11 Chemistry worksheet covering fundamental concepts of heat of formation, Hess's Law, and standard enthalpy changes of reactions.
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Standards
Heat of Formation
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Read each question carefully and provide the best possible answer. Show all your work for calculations.
1. Which of the following statements best defines the standard enthalpy of formation (ΔH°f)?
The heat released or absorbed when 1 mole of a compound is formed from its elements in their standard states.
The energy required to break all the bonds in 1 mole of a compound.
The enthalpy change when 1 mole of a substance dissolves in water.
The heat capacity of 1 mole of a substance at constant pressure.
2. For which of the following substances is the standard enthalpy of formation (ΔH°f) equal to zero?
H₂O(l)
CO₂(g)
O₂(g)
NaCl(s)
3. The enthalpy change for a reaction is independent of the pathway taken, according to .
4. A reaction with a negative ΔH is called an reaction, meaning it releases heat.
5. Calculate the standard enthalpy change (ΔH°rxn) for the following reaction using the given standard enthalpies of formation:
2H₂S(g) + 3O₂(g) → 2SO₂(g) + 2H₂O(l)
Given:
ΔH°f [H₂S(g)] = -20.6 kJ/mol
ΔH°f [SO₂(g)] = -296.8 kJ/mol
ΔH°f [H₂O(l)] = -285.8 kJ/mol
6. The standard enthalpy of formation of an element in its most stable allotropic form at 298 K and 1 atm is always zero.
True
False
7. Analyze the energy diagram below and determine if the reaction is endothermic or exothermic, and justify your answer.
