_{Up Learn – A Level Chemistry (aqa) – Thermodynamics}

_{Up Learn – A Level Chemistry (aqa) – Thermodynamics}

**Entropy Change Formula: Calculating Entropy Changes**

**How to calculate entropy change using standard molar entropies.**

### More videos on Thermodynamics:

Positive and Negative Entropy Changes

Predicting Entropy Changes of Reactions

Entropy change formula: Calculating Entropy Changes

Why are the units of entropy change ‘per mole’?

Gibbs Free Energy: Why do some Feasible Reactions not happen?

Units of Gibbs Free Energy Change

Calculating Gibbs Free Energy Change

Gibbs Free Energy: Feasibility

Finding Entropy and Enthalpy from Gibbs vs. Temperature Graph

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## Thermodynamics

2. Order and Disorder

3. What is Entropy?

4. How Does Temperature Affect Entropy?

5. How Does State Change Affect Entropy?

6. Comparing Entropy Between Substances?

6. How Does Dissolving a Substance Affect Entropy?

8. How Does the Number of Particles Affect Entropy?

9. Entropy Changes

10. Predicting the Entropy Change of a Reaction 1

11. Predicting the Entropy Change of a Reaction 2

2. A Simple System 1

3. A Simple System 2

4. Relating Configurations to Entropy

5. The Exact Mathematical Definition of Entropy

6. Relating Our Simple System to Atomic Systems

7. Why Does Temperature Affect Entropy?

8. Why Does Number of Particles Affect Entropy?

9. Why Does State Affect Entropy?

10. So Is Entropy Really a Measure of Disorder?

2. Measuring Entropy for Larger Systems

3. Entropy at Absolute Zero

4. Explaining Entropy at 0 K Mathematically

5. Entropy at Non-Zero Temperatures

6. Graphing Entropy

7. Standard Molar Entropies

8. Investigating the Trends in the Table of Absolute Entropies

9. Calculating the Entropy Change of a Reaction

10. Why Did We Bother Predicting Entropy Changes in the First Place?

11. Why Are the Units of Entropy Change ‘Per Mole’?

2. The Entropy Change of the Surroundings

3. Calculating the Entropy Change of the Surroundings

4. The Entropy Change of the Universe

5. What Reactions Can’t Happen?

6. Feasibility

7. Why Do Some Feasible Reactions Not Happen?

8. The 2nd Law of Thermodynamics

9. Gibbs Free Energy Change

10. The Units of Gibbs Free Energy Change

11. Calculating Gibbs Free Energy Change

12 .Assessing Feasibility

13. Assessing Feasibility – Making Ice

14. Assessing Feasibility – Thermal Decomposition of Calcium Carbonate

15. Exam Technique: Explaining Feasibility

16. Graphing Gibbs Free Energy Change

17. Using Graphs to Find Enthalpy and Entropy Changes

18. Assessing Feasiblility from Graphs

19. Finding the Temperature Where Reactions Become Feasible

20. The Limitations of Our Temperature-Finding Equation

21. Doesn’t Entropy Change…. Change With Temperature?

22. Calculating Gibbs Free Energy Change for Reverse Reactions

23. What About Reversible Reactions?

24. How Are Reversible Reactions Compatible With the Second Law of Thermodynamics?

Last time we looked at tables of standard molar entropies

And, now that we’ve seen what they are and how to use them, that means we can finally

move from predicting entropy changes to actually calculating them!

For example, say we wanted to find the entropy change of this reaction [N_{2} + 3H_{2} → 2NH_{3}]

We would use this table of values to find the total entropy of the products, which is…

And then use the same table to find the total entropy of the reactants, which is…

And subtract one from the other, to give this.

And this approach doesn’t just work for this reaction

In fact, to find the entropy change of any reaction, we just need to find the sum of entropies of the products

which we represent like this [ΣS _{products}]

…and subtract the sum of entropies of the reactants

which we represent like this [ΣS _{reactants}]

So, using this equation and this table , what’s the entropy change of this reaction? [H_{2}(g) + Cl_{2}(g) → 2HCl (g)]

The total entropy of the products is this [pause]

The total entropy of the reactants is this [pause]

And so the entropy change of this reaction is this [pause]

And what about this reaction? [CH_{4}(g) + 2O_{2}(g) → CO_{2}(g)+ 2H_{2}O (g) ]

The total entropy of the products is this [pause]

The total entropy of the reactants is this [pause]

And so the entropy change of this reaction is this [pause]

So, to sum up…

To calculate the entropy change of any reaction, we can use this formula

Where this [ΣS^{⊖}_{products}]represents the sum of the entropies of the products

And this [ΣS^{⊖}_{reactants}] represents the sum of the entropies of the reactants