Heat of Formation Worksheet

Heat of Formation Worksheet

Read each question carefully and answer to the best of your ability. Show all work for calculations.

1. The standard enthalpy of formation (ΔH°f) is defined as the enthalpy change when one mole of a compound is formed from its constituent elements in their   states at standard conditions (298 K and 1 atm).

2. For any element in its standard state, the standard enthalpy of formation is  .

3. An exothermic reaction has a   ΔH value, indicating that heat is   into the surroundings.

1. Which of the following equations represents the standard enthalpy of formation for liquid water?

2. The enthalpy change for the reaction: C(s, graphite) + O₂(g) → CO₂(g) is -393.5 kJ/mol. What does this value represent?

1. Explain why the standard enthalpy of formation of O₂(g) is 0 kJ/mol, but the standard enthalpy of formation of O(g) is not 0 kJ/mol.

2. How can Hess's Law be used to calculate the enthalpy of a reaction using standard enthalpies of formation?

1. Calculate the standard enthalpy change (ΔH°rxn) for the combustion of methane (CH₄) given the following standard enthalpies of formation:

CH₄(g): -74.8 kJ/mol

CO₂(g): -393.5 kJ/mol

H₂O(l): -285.8 kJ/mol

The balanced chemical equation is: CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(l)

2. Given the following reaction and its standard enthalpy change:

2FeO(s) + ½O₂(g) → Fe₂O₃(s) ΔH°rxn = -272.0 kJ/mol

And the standard enthalpy of formation for FeO(s) is -272.0 kJ/mol. Calculate the standard enthalpy of formation for Fe₂O₃(s).

1. The standard enthalpy of formation of a compound is always negative.

2. An endothermic reaction absorbs heat from the surroundings.