Enthalpy Stoichiometry Worksheet
Grade 12 Chemistry worksheet focusing on enthalpy changes in stoichiometric calculations, including Hess's Law and standard enthalpies of formation.
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Enthalpy Stoichiometry
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Read each question carefully and answer to the best of your ability. Show all your work for calculations.
1. Define enthalpy and explain its significance in chemical reactions.
2. An exothermic reaction releases heat to the surroundings, resulting in a ΔH value.
3. 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.
4. Which of the following statements is true regarding standard enthalpy of formation (ΔH°f)?
It is the enthalpy change when one mole of a compound is formed from its elements in their standard states at 1 atm and 25°C.
It is always a positive value.
It refers to the enthalpy change for any reaction that produces one mole of a compound.
It is only applicable to reactions at 0°C.
5. 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
C₂H₂(g) + ⁵⁄₂O₂(g) → 2CO₂(g) + H₂O(l) ΔH = -1300 kJ/mol
Calculate the standard enthalpy of formation (ΔH°f) for C₂H₂(g) using Hess's Law.
6. In an endothermic reaction, the products have lower enthalpy than the reactants.
True
False
7. Calculate the heat released when 50.0 g of methane (CH₄) is completely combusted, given that the standard enthalpy of combustion for methane is -890.3 kJ/mol.