Heats and Rates of Reaction - Lesson 4 - Homework Answers

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Heats and Rates of Reaction – Lesson 4 – Homework Hess’s Law Problem #1: Use the following data to determine the enthalpy (ΔH°) of reaction for: NO2(g) + (7/2) H2(g) ---> 2H2O(l) + NH3(g) ΔH° = ??? kJ Using the following two equations: 2NH3(g) ---> N2(g) + 3H2(g)

ΔH° = +92 kJ

(1/2) N2(g) + 2H2O(l) ---> NO2(g) + 2H2(g) ΔH° = +170 kJ

Problem #2: Calculate the enthapy for the following reaction: N2(g) + 2O2(g) ---> 2NO2(g) ΔH° = ??? kJ Using the following two equations: N2(g) + O2(g) ---> 2NO(g)

ΔH° = +180 kJ

2NO2(g) ---> 2NO(g) + O2(g) ΔH° = +112 kJ

Problem #3: During discharge of a lead-acid storage battery, the following chemical reaction takes place: Pb + PbO2 + H2SO4 ---> PbSO4 + H2O (balance first) Using the following two reactions: (1) Pb + PbO2 + 2SO3 ---> 2PbSO4 ΔH° = -775 kJ (2) SO3 + H2O ---> H2SO4

ΔH° = -113 kJ

Determine the enthalpy of reaction for the discharge reaction above.

Problem #4: Given the following information: 2NO(g) + O2(g) ---> 2NO2(g)

ΔH = -116 kJ

2N2(g) + 5O2(g) + 2H2O(l) ---> 4HNO3(aq) ΔH = -256 kJ N2(g) + O2(g) ---> 2NO(g)

ΔH = +183 kJ

Calculate ΔHrxn for the formation of one mole of dinitrogen pentoxide from its elements in their stable state. (b) What would the ΔH be for the formation of two moles of dinitrogen pentoxide.

Problem #5: Calculate the value of ΔH°rxn for the following reaction: P4O10(s) + PCl5(g) ---> Cl3PO(g) (balance first) using the following four equations: a) P4(s) + 6Cl2(g) ---> 4PCl3(g)

ΔH° = -1225.6 kJ

b) P4(s) + 5O2(g) ---> P4O10(s)

ΔH° = -2967.3 kJ

c) PCl3(g) + Cl2(g) ---> PCl5(g)

ΔH° = -84.2 kJ

d) PCl3(g) + (1/2)O2(g) ---> Cl3PO(g) ΔH° = -285.7 kJ

Use the standard molar enthalpies of formation to solve the following problems: Problem #6: Calculate the standard enthalpy of combustion for the following reaction: C2H5OH (l) + (7/2) O2 (g) ---> 2 CO2 (g) + 3 H2O (l)

Problem #7: Calculate the standard enthalpy of combustion for the following reaction: C6H12O6 (s) + 6 O2 (g) ---> 6 CO2 (g) + 6 H2O (l) To solve this problem, we must know the following ΔH°f values: (note: ΔH°f of C6H12O6(s) is 1275 kJ/mol)

Problem #8: Complete combustion of 1.00 mol of acetone (C3H6O) liberates 1790 kJ: C3H6O (l) + 4 O2 (g) ---> 3 CO2 (g) + 3 H2O (l); ΔH°comb, acetone = -1790 kJ Using this information together with the enthalpy of formation for CO2(g) and H2O(g) (values in kJ/mol), calculate the enthalpy of formation of acetone.

Problem # 9: Using standard enthalpies of formation, calculate the heat of combustion per mole of gaseous water formed during the complete combustion of ethane gas.