Edexcel IAL Chemistry 12.6 Total entropy change
Write ΔStotal = ΔSsystem + ΔSsurroundings, convert kJ and J before adding and retain the sign and J K⁻¹ mol⁻¹ units in the final value.
- Syllabus
- First assessment 2019
- Course
- Chemistry YCH11
- Level
- A2
Exam points
- Calculate ΔStotal by adding system and surroundings entropy changes with signs and units.
- Rearrange the total-entropy equation to find a missing system or surroundings value.
12.6—The total entropy change of any reaction is the sum of the entropy change of the system and the entropy change of question 1
[Maximum number: 1]
Ammonia is manufactured in the Haber Process.
N2( g)+3H2( g)⇌2NH3( g)
In this process, pressures between 100 atm and 300 atm and temperatures between 675 K and 725 K are usually used.
At 700 K, the total entropy change, ΔS_total = -78.7 J K⁻¹ mol⁻¹. Calculate ΔS_system for this reaction at 700 K. Include a sign and units in your answer.
Finds ΔS_system: ΔS_system = ΔS_total - ΔS_surroundings = -78.7 - 157.4 = -236.1 / -236 J K⁻¹ mol⁻¹, or -0.236 kJ K⁻¹ mol⁻¹. Allow transfer error from (a)(iii).
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