The equation for the formation of ammonia in the Haber Process is shown
1⁄2N2 (g) +1 1⁄2H2 (g) ⇌ NH3 (g)
At 298 K the standard entropy change of the system, = –98 JK–1mol–1.
Calculate the standard entropy of one mole of ammonia.
Use the value of and the data in the table.
Substance | Standard molar entropy, /JK–1mol–1 |
N2 | 192 |
H2 | 131 |
The value of the total entropy change, ΔStotal , varies with temperature.
Data for the value of ΔStotal at different temperatures but at standard pressure of 100 kPa are given for this reaction.
Temperature / K | 1/T / K–1 | ΔStotal / kJ K–1mol–1 |
250 | 4.00×10–3 | 8.27×10–2 |
375 | 2.67×10–3 | 2.25×10–2 |
500 | 2.00×10–3 | –0.764×10–2 |
625 | 1.60×10–3 | –2.57×10–2 |
750 | 1.33×10–3 | –3.77×10–2 |
Plot a graph of ΔStotal against 1/T on the grid.
Include a line of best fit.
The relationship between ΔStotal and 1/T can be found by combining the two equations:
to give
Determine the gradient of the line plotted in (b), including units in your answer.
(1)
(1)
(1)
The industrial synthesis of ammonia
1⁄2N2 (g) +1 1⁄2H2 (g) ⇌ NH3 (g)
is carried out at pressures of about 20000kPa and temperatures between 700 K and 750 K. These temperatures are higher than the answer to (c)(iii).
State the relationship between the total entropy, ΔStotal , and the equilibrium constant, K.
(1)
[ΔStotal at 750K = –37.7JK–1 mol–1]
(2)
Explain why ΔStotal decreases with an increase in temperature.
(3)
State how the Haber Process is made economically feasible at 750 K even though the total entropy change is negative.
(1)
Ammonia from the Haber Process reacts with acids.
With phosphoric acid, H3PO4, a number of products are formed in solution.
One of these is the fertiliser diammonium hydrogenphosphate.
Write an equation for the production of this fertiliser.
State symbols are not required.
(2)
Write an ionic equation to show that ammonium ions are acidic in aqueous solution.
State symbols are not required.
(1)
A solution containing both ammonia and ammonium ions acts as a buffer.
Explain, using a relevant ionic equation, the effect of adding a small amount
of acid to this buffer.
(3)
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