Thermochemistry

A 0.1326 g sample of magnesium was burned in an oxygen bomb calorimeter. The total heat capacity of the calorimeter plus water was 5,760 J/°C. If the temperature rise of the calorimeter with water was 0.570°C, calculate the enthalpy of combustion of magnesium.

Mg(s) + 1/2O₂(g) → MgO(s)

(A) –3280 kJ/mol

(B) –24.8 kJ/mol

(C) 435 kJ/mol

(D) 106 kJ/mol

(E) –602 kJ/mol

Given the thermochemical equation 2SO₂(g) + O₂(g) → 2SO₃(g), ΔH°_rxn= –198 kJ/mol, how much heat is evolved when 600. g of SO₂ is burned?

(A) 5.46 x 10^–2 kJ

(B) 928 kJ

(C) 1.85 x 10³ kJ

(D) 59,400 kJ

(E) 3.71 x 10³ kJ

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 

A glass containing 200. g of H₂O at 20°C was placed in a refrigerator. The water loses 11.7 kJ as it cools to a constant temperature. What is its new temperature? The specific heat of water is 4.184 J/g·°C. 

(A) 0.013°C 

(B) 4°C 

(C) 6°C 

(D) 14°C 

(E) 34°C

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

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

How much heat is required to raise the temperature of 2,500 g of water from 27°C to 72°C? The specific heat of water is 4.184 J/g·°C. 

(A) 0.19 kJ 

(B) 10. kJ 

(C) 280 kJ 

(D) 470 kJ 

(E) 750 kJ

At 25°C, the standard enthalpy of formation of anhydrous sodium carbonate is –1130.9 kJ/mol, whereas the standard enthalpy of formation of sodium carbonate monohydrate is –1430.1 kJ/mol. Determine ΔH° at 25°C for the reaction

Na₂CO₃(s) + H₂O(l) → Na₂CO₃·H₂O(s).

(Given: ΔH°_f[H₂O(l)] = –285.8 kJ/mol)

(A) –13.4 kJ/mol

(B) –285.8 kJ/mol

(C) –585.0 kJ/mol

(D) –299.2 kJ/mol

(E) –156.3 kJ/mol

An endothermic reaction causes the surroundings to 

(A) warm up. 

(B) become acidic

(C) condense.

(D) decrease in temperature.

(E) release CO₂.