Edexcel IAL Chemistry 6.1 Enthalpy change and standard conditions

Check temperature and pressure against the standard values before deciding whether the measured energy change can be reported as a standard molar enthalpy.

Exam points

State standard enthalpy conditions as 298 K and approximately 100 kPa pressure.
Explain why non-standard temperature data cannot give a standard molar enthalpy.

[Maximum number: 1]

Fuels

Fuels burn in oxygen to release a lot of energy.
Many hydrocarbons and alcohols are used as fuels. During complete combustion, they produce carbon dioxide and water.

Petrol contains 2,2,4-trimethylpentane, an isomer of octane, that promotes smooth combustion.

Figure for Question 6.1—The enthalpy change, ∆H, is the heat energy change measured at constant pressure and that standard conditions are 100 kPa question 1 — Edexcel A-Level Chemistry AS

2,2,4-trimethylpentane

Alcohols, such as methanol and ethanol, can be used as fuels either on their own or as additives in petrol.

The standard enthalpy change of combustion, $\Delta_{\mathrm{c}} H^{\ominus}$ , of 2,2,4-trimethylpentane is $-5461 \mathrm{~kJ} \mathrm{~mol}^{-1}$ .

State the two standard conditions for this enthalpy change.

All question bank results loaded

6.1—The enthalpy change, ∆H, is the heat energy change measured at constant pressure and that standard conditions are 100 kPa question 1