8. Thermochemistry

Which statement best explains how the enthalpy of formation is used to predict whether a chemical reaction is endothermic or exothermic?

In the context of enthalpy of formation, what does the difference between the enthalpies of the products and the reactants represent?

Which of the following substances has a standard enthalpy of formation (ΔH_f^ext{∘}) defined as 0 kJ/mol?

Given the reaction: C_2H_4 + H_2O → C_2H_5OH, what is the enthalpy change for this reaction in terms of standard enthalpies of formation (ΔH_f^ext{°})?

Using the standard enthalpies of formation, calculate ΔH°rxn for the reaction: CaO(s) + CO2(g) → CaCO3(s). Given: ΔH°f [CaO(s)] = -635.1 kJ/mol, ΔH°f [CO2(g)] = -393.5 kJ/mol, ΔH°f [CaCO3(s)] = -1206.9 kJ/mol.

Which statement about the standard enthalpy of formation (ΔH_f^ext{∘}) is true?

Given the following chemical reaction: 2H2(g) + O2(g) → 2H2O(l), which of the following best describes how to calculate the enthalpy change (ΔH) for the overall reaction using standard enthalpies of formation?

Which of the following substances has a standard enthalpy of formation (ΔH_f^∘) of zero at 298 K?

For which of the following reactions does ΔH_{rxn} represent an enthalpy of formation?

The enthalpy of formation of water is –285.8 kJ/mol. What does this value indicate?

Which of the following substances has a standard enthalpy of formation equal to zero at 25°C and 1 atm?