Entropy & Spontaneity

15.2 Entropy and spontaneity

Understandings

Entropy (S) refers to the distribution of available energy among the particles. The more ways the energy can be distributed the higher the entropy.
Gibbs free energy (G) relates the energy that can be obtained from a chemical reaction to the change in enthalpy (H), change in entropy (S), and absolute temperature. Guidance: G is a convenient way to take into account both the direct entropy change resulting from the transformation of the chemicals, and the indirect entropy change of the surroundings as a result of the gain/loss of heat energy. Examine various reaction conditions that affect G.
Entropy of gas > liquid > solid under same conditions.

Applications and skills

Prediction of whether a change will result in an increase or decrease in entropy by considering the states of the reactants and products.
Calculation of entropy changes (S) from given values (S ).
Application of G = H – TS in predicting spontaneity and calculation of various conditions of enthalpy and temperature that will affect this. Guidance: Thermodynamic data are given in section 12 of the data booklet.
Relation of G to position of equilibrium.

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Flipped classroom

Entropy overview

Task:
1. Watch the task
2. Think about and research real world example of entropy increasing
3. Find a picture or video of the real world example and explain what is happening using the second law of thermodynamics
4. Add your pictures/videos and explanation on the wakelet below

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Spontaneity and Gibbs free energy

Task:

1. Watch the video and complete the check for comprehension question
2. Think about, explain and calculate why water melts at 0°C - follow the step by step process below

Give an equation for the melting of water
Predict the sign for the entropy change and enthalpy change for this process
Predict a value for the sign of Change in Gibbs free energy at low and high temperatures
Suggest why water melts at 0°C
Calculate the entropy change

Entropy: H2O (s) = -44.8 J K-1 mol-1 I H2O (l) = +70.0 J K-1 mol-1

Calculate the enthalpy change

Enthalpy of formation: H2O (s) = -241.82kJ/mol I H2O (l) = -286kJ/mol

Deduce the melting point of water. Describe any assumptions that you have made

3. Create a poster and explain the process using the Flipgrid below.

Sources:
http://www1.lsbu.ac.uk/water/water_properties.html
https://www.quora.com/Why-is-the-std-enthalpy-change-of-formation-for-H2O-l-more-exothermic-than-that-of-H2O-g

Flipped Classroom

Determining spontaneity of a reaction

Task:
1. Watch the videos
2. Consider the reaction below when determining the spontaneity of a reaction

∆G = ∆H - T∆S

3. Take the quiz below. Use the equation above to help you.