Question

The combustion of gasoline (C_8H_{18}) leads to a change in internal energy, \DeltaU of 5404 kJmol^{–1} at 298.0 K. What is the corresponding change in enthalpy, \DeltaH?

Answer 1

-5426.30 kJ mol⁻¹ is the corresponding change in enthalpy.

Explanation:

The balanced reaction of combustion of C₈H₁₈ can be written as:

• $2C_{8}H_{18} + 25O_{2} \rightarrow 16CO_{2} + 18H_{2}O$

Given:

• ΔU = 5404 kJ mol⁻¹
• T = 298 K
• ΔH =?

To find the corresponding change in enthalpy, we can use the following formula:

• $\Delta U = \Delta H - RT\Delta n$

where Δn is the difference between the number of moles of gaseous product and gaseous reactants.

• $\Delta H = -RT\Delta n -\Delta U$
• $\Delta H = -(0.008314\times 298 \times 9) - 5404$
• ΔH = -5426.30 kJ mol⁻¹