Thermochemistry

Methanol (CH₃OH) burns according to the equation

2CH₃OH(l) + 3O₂(g) → 2CO₂(g) + 4H₂O(l), ΔH°_rxn = –1454 kJ/mol.

How much heat, in kilojoules, is given off when 75.0 g of methanol is burned?

(A) 727 kJ

(B) 3.22 x 10³ kJ

(C) 1.45 x 10³ kJ

(D) 1.70 x 10^–3 kJ

(E) 3.41 x 10³ kJ

How many degrees of temperature rise will occur when a 25.0 g block of aluminum absorbs 10.0 kJ of heat? The specific heat of Al is 0.900 J/g·°C. 

(A) 0.44°C 

(B) 22.5°C 

(C) 225°C 

(D) 360°C 

(E) 444°C

To which one of the following reactions occurring at 25°C does the symbol ΔH°_f[HNO₃(l)] refer?

(A) H(g) + N(g) + O₃(g) → HNO₃(l) 

(B) (1/2)H₂(g) + (1/2)N₂(g) + (3/2)O₂(g) → HNO₃(l) 

(C) HNO₃(l) → (1/2)H₂(g) + (1/2)N₂(g) + (3/2)O₂(g) 

(D) HNO₃(l) → H(g) + N(g) + 3O(g) 

(E) H₂(g) + N₂(g) + O₃(g) → HNO₃(l)

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

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)

Aluminum oxide can be reduced to aluminum metal using carbon, the other reaction product being carbon monoxide. Determine the enthalpy change when 12.5 g of aluminum is produced by this method. [ΔH°_f(carbon monoxide) = –110.5 kJ/mol; ΔH°_f(aluminum oxide) = –1669.8 kJ/mol] 

(A) 725 kJ 

(B) 697 kJ 

(C) 310 kJ 

(D) 361 kJ 

(E) 1504 kJ

Calculate the amount of work done, in joules, when 2.5 mole of H₂O vaporizes at 1.0 atm and 25°C. Assume the volume of liquid H₂O is negligible compared to that of vapor. (1 L·atm = 101.3 J) 

(A) 6,190 kJ 

(B) 6.19 kJ 

(C) 61.1 J 

(D) 5.66 kJ 

(E) 518 J

Octane (C₈H₁₈) undergoes combustion according to the following thermochemical equation:

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

Given that Δ H°_f[CO₂(g)] = –393.5 kJ/mol and ΔH°_f[H₂O(l)] = –285.8 kJ/mol, calculate the standard enthalpy of formation of octane.

(A) –210 kJ/mol

(B) –11,230 kJ/mol

(C) 22,040 kJ/mol

(D) –420 kJ/mol

(E) 420 kJ/mol 

The combustion of butane produces heat according to the equation 

2C₄H₁₀(g) + 13O₂(g) → 8CO₂(g) + 10H₂O(l) ΔH°_rxn = –5,314 kJ/mol 

What is the heat of combustion per gram of butane?

(A) –32.5 kJ/g

(B) –45.7 kJ/g

(C) –91.5 kJ/g

(D) –2,656 kJ/g

(E) –15,440 kJ/g

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