The correct answer is B because:

The ideal gas equation is pV = nRT
- Where p is pressure (Pa), V is the volume (m³), n is the number of moles, R is the gas constant (8.31 J K⁻¹ mol⁻¹), and T is the temperature (K)

Rearranged for pressure:
- p = $\frac{nRT}{V}$

Number of moles of nitrogen:
- $moles (n) = \frac{mass (m)}{molar mass (M_{r})}$ = $\frac{0.89}{28}$ = 0.031786 mol

Known quantities:
- Number of moles; 0.031786 mol
- Volume; 7.0 × 10⁻³ m³
- Temperature; 305 K

Substitution into the equation:
- p = $\frac{nRT}{V}$ = $\frac{0.031786 \times 8.31 \times 305}{7.0 \times 10^{- 3}}$ = 11508.92 Pa

Don’t forget to rearrange pV = nRT correctly to make pressure the subject of the equation.

You need to calculate the number of moles reacting and then check if all the variables have the correct units, which in this question they do.

C is an example of an answer where a student has converted Pa into kPa and has divided their final answer by 1000, which is incorrect as pressure in Ideal Gas equations is always quoted in Pa.

The Mole, Avogadro & The Ideal Gas Equation (AQA A Level Chemistry)

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