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Edexcel IAL Chemistry 12.8 Surroundings and total entropy

Use ΔSsurroundings = −ΔH/T with T in kelvin and matching joule units, retain the enthalpy sign and then add the system contribution.

Syllabus
First assessment 2019
Course
Chemistry YCH11
Level
A2

Exam points

  • Calculate ΔSsurroundings = −ΔH/T after converting kJ to J and temperature to K.
  • Combine system and surroundings values to obtain total entropy with sign and units.
  • Rearrange the surroundings equation to calculate enthalpy from entropy and temperature.

12.8—The entropy change in the surroundings, and hence ∆Stotal question 1

[Maximum number: 1]

The equation for the formation of ammonia in the Haber Process is shown

1/2 N2( g)+112H2( g)⇌NH3( g)1 / 2 \mathrm{~N}_{2}(\mathrm{~g})+1 \frac{1}{2} \mathrm{H}_{2}(\mathrm{~g}) \rightleftharpoons \mathrm{NH}_{3}(\mathrm{~g})

The relationship between ΔStotal \Delta S_{\text {total }} and 1 / T can be found by combining the two equations:

ΔStotal =ΔSsurroundings +ΔSsystem \Delta S_{\text {total }}=\Delta S_{\text {surroundings }}+\Delta S_{\text {system }}

and ΔSsurroundings =−ΔH/T\Delta S_{\text {surroundings }}=-\Delta H / T
to give

ΔStotal =−ΔH/T+ΔSsystem \Delta S_{\text {total }}=-\Delta H / T+\Delta S_{\text {system }}

Identify the thermodynamic quantity that can be obtained from this gradient.

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