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What makes a reaction feasible or spontaneous? How do you calculate entropy change of system, entropy change of surroundings and entropy change of the universe? All this and more covered in this comprehensive lesson with questions and answers! This is a Year 13 A level lesson for Edexcel International Unit 4 – WCH14, but it can also be used for all UK exam boards. All the slides in this lesson are fully animated and include answers to every mini plenary question and exam question. The breakdown of the slides (which are best opened on Microsoft PowerPoint) is as follows:

Slide 1 - Title and 5-minute starter. The starter is a grid of four questions entitled ‘last week, last lesson, today’s learning and future learning’. Use this generic slide for all of your lessons by simply changing the questions and the answers each time.
Slide 2 - Lesson objectives (see thumbnail image)
Slides 3 – 6: Introduction to total entropy change, including definitions and visuals for entropy change of system and entropy change of surroundings
Slides 4 – 6 Learning question: Why is the reaction between magnesium and oxygen spontaneous, energetically speaking?
Slide 7 – Introduction of new knowledge that forms the bedrock of the lesson: For a reaction to be spontaneous, Δ𝑆𝑡𝑜𝑡𝑎𝑙 must be positive
Slides 8 – 17: Entropy change of system. There are two worked examples (with printout slides included) for you to go through with the students. The answers animate onto the screen as you click.
Slides 18 – 20: Mini plenary (Learning pit-stop). A set of questions for students to practise calculating entropy change of system. Answers animate as you click!
Slides 21 – 29: Entropy change of surroundings and total entropy change. There are two worked examples (with printout slides included) for you to go through with the students. The last example gives students an opportunity to calculate the total entropy change. The answers animate onto the screen as you click.
Slides 30 – 33: Word fill exercise about entropy change of system, surroundings and total entropy change. Answers animate onto the screen as you click.
Slide 34 – Which temperature does a reaction become feasible?
Slides 35 – 38 (hidden in slideshow mode): Using the Gibbs’ equation to work out feasibility. Teach at your discretion – this approach is allowed to work out the temperature at which a reaction becomes feasible, but it is not a requirement for the International A level
Slides 39 - 41: Using T = ΔH÷ΔS_system to work out the temperature of feasibility
Slides 42 – 44: Mini plenary (Learning pit-stop). A set of questions for students to practise calculating temperature of feasibility. Answers animate as you click!
Slide 45 – consideration of thermodynamic and kinetic stability
Slides 46 – 51: Exam questions with mark scheme answers (included with the resource)

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