Skip to content
Clear highlightsClear Highlight Report a problem

Hess's Law

If a reaction can take place by two routes the total enthalpy change for each route is the same provided that the starting and finishing conditions are the same.Hess's Law is a consequence of the law of Conservation of Energy.In the following reactions, ΔHr = ΔHc(carbon) + ΔHc (hydrogen) - ΔHc(ethanol), taking the combustion enthalpies of carbon and hydrogen for 2 mol of C and 3 mol of H2

Read the text

Read the text and highlight anything you think is important. When you go on, the text is hidden and you answer from memory.

Next

Specification: OCR Chemistry A (H032), AS-level, 3.2.1 Enthalpy changes. Topic: Enthalpy.

Key terms in this lesson

Enthalpy
A measure of the total energy of a chemical system.
Enthalpy change
The heat energy that is transferred between the system and its surroundings during a process carried out at constant pressure.

More in Enthalpy

All 19 lessons in Enthalpy · All OCR AS-level Chemistry topics