Edexcel IAL Chemistry Slope and Intercept

Practise Edexcel IAL Chemistry slope skills by finding gradients from best-fit graph lines, showing graph working and attaching units when required.

Exam points

Calculate gradients from best-fit graph lines using two points on the line and show working on the graph.
Attach appropriate units to gradients when axes carry quantities such as entropy change and reciprocal temperature.

[Maximum number: 1]

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

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

\Delta S_{\text {total }}=\Delta S_{\text {surroundings }}+\Delta S_{\text {system }}

and $\Delta S_{\text {surroundings }}=-\Delta H / T$
to give

\Delta S_{\text {total }}=-\Delta H / T+\Delta S_{\text {system }}

Determine the gradient of the line plotted in (b), including units in your answer.

An answer that makes reference to the following points:

- uses the line or points from the data to calculate the gradient and units

Example of calculation
$\text { Gradient }=\frac{8.27 \times 10^{-2}--0.76 \times 10^{-2}}{4.00 \times 10^{-3}-2.00 \times 10^{-3}}$ $=45.15 \mathrm{~kJ} \mathrm{~mol}^{-1}$
Allow an answer between 42.0-48.0
Ignore SF except 1 SF

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B.3.3—Slope and intercept of a linear graph question 1