Question

Part A

When 2.275 g of anthracene, C₁₄H₁₀, is combusted in a bomb calorimeter that has a water jacket containing 500.0 g of water, the temperature of the water increases by 43.15°C. Assuming that the specific heat of water is 4.18 J/(g • °C), and that the heat absorption by the calorimeter is negligible, estimate the enthalpy of combustion per mole of anthracene.

Part B

The specific heat capacity of methane gas is 2.20 J/g• K. How many joules of heat are needed to raise the temperature of 5.00 g of methane from 20.0°C to 44.1°C?

Part C

Use the ΔH°_f and ΔH°_rxn information provided to calculate ΔH°_f for SO₃(g):

2 SO₂(g) + O₂(g) → 2 SO₃(g) ΔH°_rxn = -198 kJ

	ΔH°f (kJ/mol)
SO2(g)	-297

Answer 1

Part A :

Heat absorbed by water , Q = mcdt

Where

m = mass of water = 500.0 g

c = specific heat capacity of water = 4.18 J/goC

dt = raise in temperature = 43.15oC

Plug the values we get Q = 90.183x10³ J

= 90.183 kJ

This Q is supplied by 2.275 g of C14H10

Number of moles of C14H10 = mass/molar mass = 2.275g / 178 g/mol = 0.0128 mol

So enthalpy of combustion per mole of anthracene = 90.183 kJ/0.0128 mol = 7056 kJ/mol

Part B :

Heat neededr , Q = mcdt

Where

m = mass of methane = 5.00 g

c = specific heat capacity = 2.20 J/goC

dt = raise in temperature = 44.1-20.0 = 24.1 oC

Plug the values we get Q = 265.1 J

Part C :

2 SO2(g) + O2(g) → 2 SO3(g) ΔH°rxn = -198 kJ

ΔH°rxn =  [(2xΔH°f SO3(g) )] - [(2xΔH°f SO2(g)) +ΔH°f O2(g)]

-198 =  [(2xΔH°f SO3(g) )] - [(2x(-297))+ 0]

ΔH°f SO3(g) = 198 kJ/mol