Define heat of combustion. Write the balanced equation for the complete combustion of butane in an adequate supply of oxygen. Calculate the heat of combustion of butane, given that the heats of formation of carbon dioxide, water, and butane are −393.5, −285.8 and −127.1 kJ mol⁻¹, respectively.

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Define heat of combustion - Leaving Cert Chemistry - Question 4 - 2014

Question 4

Define heat of combustion. Write the balanced equation for the complete combustion of butane in an adequate supply of oxygen. Calculate the heat of combustion of b... show full transcript

Worked Solution & Example Answer:Define heat of combustion - Leaving Cert Chemistry - Question 4 - 2014

Step 1

Define heat of combustion.

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Answer

The heat of combustion is defined as the amount of heat energy released when one mole of a substance is burned completely in oxygen under standard conditions.

Step 2

Write the balanced equation for the complete combustion of butane.

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Answer

The balanced equation for the complete combustion of butane (C₄H₁₀) in oxygen is:

ightarrow 4 ext{CO}_2 + 5 ext{H}_2 ext{O}$$

Step 3

Calculate the heat of combustion of butane.

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Answer

To calculate the heat of combustion of butane, we use the heats of formation:

$ext{ΔH}_{comb} = ext{ΣΔH}_{f, ext{products}} - ext{ΣΔH}_{f, ext{reactants}}$

Substituting the values:

$ext{ΔH}_{comb} = [4(-393.5) + 5(-285.8)] - [-127.1]$

Calculating:

$ext{ΔH}_{comb} = [-1574 - 1429 + 127.1] = -2877.3 ext{ kJ mol}^{-1}$

Thus, the heat of combustion of butane is approximately −2877.3 kJ mol⁻¹.

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