Thermochemistry

Calculate the standard enthalpy change for the reaction

2C₈H₁₈(l) + 21O₂(g) → 8CO(g) + 8CO₂(g) + 18H₂O(l). 

Given: 

2C₈H₁₈(l) + 25O₂(g) → 16CO₂(g) + 18H₂O(l) ΔH° = –11,020 kJ/mol

2CO(g) + O₂(g) → 2CO₂(g) ΔH° = –566.0 kJ/mol

(A) 1.0454 x 10⁴ kJ/mol

(B) –8,756 kJ/mol

(C) 1.1586 x 10⁴ kJ/mol

(D) –6,492 kJ/mol 

(E) –1.0454 ´ 104 kJ/mol

If 325 g of water at 4.2°C absorbs 12.28 kJ, what is the final temperature of the water? The specific heat of water is 4.184 J/g·°C. 

(A) 4.21°C 

(B) 4.8°C 

(C) 9.0°C 

(D) 13.2°C 

(E) 2,938°C

Find the heat absorbed from the surroundings when 15 g of O₂ reacts according to the equation O + O₂ → O₃, ΔH°_rxn= –103 kJ/mol. 

(A) 4.6 x 10^–3 kJ 

(B) 48 kJ 

(C) 96 kJ 

(D) 32 kJ 

(E) 110 kJ

The heat of solution of ammonium nitrate is 26.2 kJ/mol. If a 5.368 g sample of NH₄NO₃ is added to 40.0 mL of water in a calorimeter at 23.5°C, what is the minimum temperature reached by the solution? (The specific heat of water = 4.18 J/g·°C; the heat capacity of the calorimeter = 650. J/°C.) 

(A) 14.3°C 

(B) 20.8°C 

(C) –7.7°C 

(D) 25.6°C 

(E) 21.4°C

Pentaborane B₅H₉(s) burns vigorously in O₂ to give B₂O₃(s) and H₂O(l). Calculate ΔH°_rxn for the combustion of 1 mol of B₅H₉. 

ΔH°_f[B₂O₃(s)] = –1,273.5 kJ/mol 

ΔH°_f[B₅H₉(s)] = 73.2 kJ/mol 

ΔH°_f[H₂O(l)] = –285.8 kJ/mol

(A) –1,2735 kJ/mol

(B) –4,543 kJ/mol

(C) –18,170 kJ/mol

(D) –9,086 kJ/mol

(E) –8,448 kJ/mol

For which of these reactions will the difference between ΔH° and ΔE° be the smallest? 

(A) N₂(g) + 3H₂(g) → 2NH₃(g) 

(B) 4PH₃(g) → P₄(g) + 6H₂(g) 

(C) H₂(g) + Cl₂(g) → 2HCl(g) 

(D) CO₂(g) + 2H₂O(l) → CH₄(g) + 2O₂(g) 

(E) P₄(s) + 10Cl2(g) → 4PCl₅(s)

When 0.560 g of Na(s) reacts with excess F₂(g) to form NaF(s), 13.8 kJ of heat is evolved at standard-state conditions. What is the standard enthalpy of formation (ΔH°_f) of NaF(s)?

(A) 24.8 kJ/mol

(B) 570 kJ/mol

(C) –24.8 kJ/mol

(D) –7.8 kJ/mol

(E) -570 kJ/mol

When 18.5 g of HgO(s) is decomposed to form Hg(l) and O₂(g), 7.75 kJ of heat is absorbed at standard-state conditions. What is the standard enthalpy of formation (ΔH°_f) of HgO(s)?

(A) –90.7 kJ/mol

(B) –7.75 kJ/mol

(C) 0.419 kJ/mol

(D) 27.9 kJ/mol

(E) 143 kJ/mol 

Find the standard enthalpy of formation of ethylene, C₂H₄(g), given the following data: heat of combustion of C₂H₄(g) = –1411 kJ/mol; ΔH°_f[CO₂(g)] = –393.5 kJ/mol; 

ΔH°f[H₂O(l)] = –285.8 kJ/mol.

(A) 52 kJ/mol

(B) 87 kJ/mol

(C) 731 kJ/mol

(D) 1.41 x 10³ kJ/mol

(E) 2.77 x 10³ kJ/mol