The enthalpy change for a chemical reaction is the sum of the energy consumed in

Question

The enthalpy change for a chemical reaction is the sum of the energy consumed in breaking bonds and the energy released during bond formation. One way to determine the overall energy change for a chemical reaction is to apply Hess’s law to add together a group of reactions which can be arranged such that the chemical equations, when combined, give the overall equation we are trying to characterize.

Part 3 (1 point) 9 See Hint The average propane cylinder for a residential grill holds approximately 18 kg of propane. How much energy (in kJ) is released by the combustion of 18.00 kilograms of propane in sufficient oxygen? 672034 kJ

Explanation / Answer

PART 1

balance

C3H8 + O2 = CO2 + H2O

C3H8 + O2 = 3CO2 + H2O

C3H8 + O2 = 3CO2 + 4H2O

C3H8 + 5O2 = 3CO2 + 4H2O

Part 2.

combine this to get 1 mol f porpane combustion

invert rxn 1, since we need proapne

C3H8 = 3C + 4H2 H = 103.8

multiply rxn 3, by 3, since CO2 requires 3x coeff

3C + 3O2 = 3CO2 H = 3*(-393.5) = -1180.5

mutliply H2O by 4

4H2 + 2O2 = 4H2O H = 4*(-285.8) = -1143.2

Add all

HRxn = 103.8-1180.5-1143.2 = -2219.9 kJ

Part 3

m = 18 kg = 1800 g

mol = mass/MW = 1800/44.0956 = 40.820 mol

ratio is 1 mol of propane = 1143.2 kJ

40.820 mol --> 40.82*1143.2 = 46665.424 kJ reqleased

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