Table of Contents
IB Chemistry: Spontaneity
Spontaneity
Introduction
A spontaneous reaction is often defined as “a reaction that causes a system to move from a less stable to a more stable state”. This unit will focus on this idea of spontaneity, and how we can link the previous concepts of entropy and enthalpy to Spontaneity.
- Predict whether a reaction or process will be spontaneous by using the sign of ∆G
- If ΔG < 0, then the reaction is spontaneous
- If ΔG >0, then the reaction is non-spontaneous.
- Calculate ∆G for a reaction using the equation ∆G= ∆H- T∆S and by using values of the standard free energy change of formation, ∆G
Whether a reaction is spontaneous or not depends on three factors:
- Enthalpy Change (ΔH)
- Entropy (ΔS)
- Gibbs Free Energy (ΔG)
An equation linking the these three values is:
ΔG = ΔH – T ΔS
Gibbs Free Energy = Enthalpy Change – Temperature x Entropy
Note: Temperature is measured in Kelvin, which can be calculated by 273 to the °C value you are given.
- Predict the effect of a change in temperature on the spontaneity of a reaction using standard entropy and enthalpy changes and the equation ∆G= ∆H -T∆S
I think I’ll do this problem using a table:
