Spontaneity: Factors and Predictions

University:
International Baccalaureate
Course:
IB Chemistry
Academic year:

2023
Views:

18

Pages:

2
Author:

anon

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 nonspontaneous. 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: ΔH ΔS TΔS ΔH – T ΔS Gibbs Free energy (ΔG) Spontaneou s? + + + (+) – (+) Depends on “T” If ΔH < TΔS + – – (+) – (-) + Never spontaneous – + + (-) – (+) – Always spontaneous – – – (-)-(-) Depends on “T” If ΔH > TΔS 0 + + 0 – (+) – Always spontaneous 0 – – 0-(-) + Never spontaneous

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