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Thermochemical Equations Answers

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The enthalpy of formation for C6 H6 (I) is 49.0 kJ/mol. Consider the following reaction.Is the reaction endothermic or exothermic, and what is the enthalpy of reaction? Use .

exothermic; Hrxn = 49.0 kJ

exothermic; Hrxn = –49.0 kJ

endothermic; Hrxn = 49.0 kJ

endothermic; Hrxn = –49.0 kJ

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Manganese dioxide (MnO2(s), Hf = –520.0 kJ) reacts with aluminum to form aluminum oxide (AI2O3(s), Hf = –1699.8 kJ/mol) and manganese according to the equation below.What is the enthalpy of the reaction? Use .

–1,839.6 kJ

–1,179.8 kJ

1,179.8 kJ

1,839.6 kJ

Sulfur reacts with oxygen to form sulfur dioxide (SO2(g), Hf = –296.8 kJ/mol) according to the equation below.What is the enthalpy change for the reaction? Use .

–593.6 kJ

–296.8 kJ

296.8 kJ

593.6 kJ

Which statement about Hf is true?

It is positive when the bonds of the product store more energy than those of the reactants.

It is zero for any pure substance in its standard state.

It is negative when a compound forms from elements in their standard states.

It is zero for any compound that is in the liquid state.

Ammonia (NH3 (g), Hf = –45.9 kJ/mol ) reacts with oxygen to produce nitrogen and water (H2 O(g), Hf = –241.8 kJ/mol) according to the equation below.What is the enthalpy of the reaction? Use .

–3,572.1 kJ

–1,267.2 kJ

1,267.2 kJ

3,572.1 kJ

Consider the reaction.Standard Enthalpies of FormationSubstanceDHf (kJ/mol)C2 H2 (g)226.73CaCO3 (s)–1206.92CaO (s)–635.09CO (g)–110.525CO2 (g)–393.509H 2 O (I)–285.8H 2 O (g)–241.818C (s), diamond1.895C (s), graphite0.0Based on the equation and the information in the table, what is the enthalpy of the reaction? Use .

–453.46 kJ

–226.73 kJ

226.73 kJ

453.46 kJ

The Hrxn of formation of carbon dioxide is negative. Which statement is true?

The reaction is endothermic.

The reaction is exothermic.

The amount of carbon dioxide is more than the amount of reactants.

The amount of carbon dioxide is less than the amount of reactants.

Which statement is true if the Hrxn of a reaction is positive?

The reaction is endothermic.

The reaction is exothermic.

There is more reactant than product.

There is more product than reactant.

How is enthalpy used to predict whether a reaction is endothermic or exothermic?

When the enthalpy of the reactants is higher than the enthalpy of the products, the reaction is endothermic.

When the enthalpy of the products is higher than the enthalpy of the reactants, the reaction is exothermic.

When the enthalpy change of the reaction is positive, the reaction is exothermic.

When the enthalpy change of the reaction is positive, the reaction is endothermic.

Butane C4 H10 (g),(Hf = –125.6), combusts in the presence of oxygen to form CO2 (g) (Hf = –393.5 kJ/mol), and H2 O(g) (Hf = –241.82) in the reaction: What is the enthalpy of combustion, per mole, of butane? Use .

–5,315 kJ/mol

–2,657.5 kJ/mol

2,657.4 kJ/mol

5,314.8 kJ/mol

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