Question

Consider the combustion of propane:

C3H8(g)+O2(g)→CO2(g)+H2O(g)

a). Divide all coefficients by the coefficient on propane, so that you have the reaction for the combustion of 1 mole of propane.

Express your answer as a chemical equation. Identify all of the phases in your answer.

b). ΔHrxn for the combustion of one mole of propane is −2219kJ. What mass of propane would you need to burn to generate 6.0 MJ of heat?

Express your answer to two significant figures and include the appropriate units.

c). If propane costs about $0.67/L and has a density of 2.01 g/cm3 how much would it cost to generate 6.0 MJ of heat by burning propane?

Express your answer using two significant figures.

Answer 1

a) THE BALANCED CHEMICAL EQUATION IS: C₃H₈(g) + 5O₂(g) ---> 3CO₂ (g) + 4H₂O(g)

All phases are gases

b) As the molar heat of combustion of propane is -2219 kJ,

molar mass of propane = 44 g/mol

so, burning 44 g of propane, will release heat = 2219 kJ

or, 2219 kJ of heat can be obtained by burning propane = 44g

6 MJ of heat can be obtained by propane = 44X6 MJ/2219 kJ = 118.97 g { M = 1000000 and k = 1000}

= 0.12 kg

c) density of propane = 2.01 g/cm3 = 2.01 kg/L

therfore, now we can convert mass of propane into required volume

2.01 kg of propane has volume = 1 L

so, 0.12 kg will have the volume = 0.12/2.10 = 0.0597 L

now we can calculate the cost, the rate is $0.67/L

for 0.0597 L, the amount would be = $0.67X0.0597 = $ 0.04