2020 P1 Q6 - Compare PV against V Graph of Equal Masses of Gases

Let's take a look at 2020 A Levels H2 Chemistry Paper 1 Question 6.

2020 p1 q6 question

We are required to determine which graph shows the results for neon.

Let us first consider the shape of PV against V graph for an ideal gas.

2020 p1 q6 deduce shape of pv against v graph

From Ideal Gas Equation

PV = nRT

Gas constant R and temperature T are constants and for each gas, number of moles n will also be constant.

This means nRT is a constant and we can write the Ideal Gas Equation as

PV = nRT = k

The graph of PV against V will be a horizontal line, and the y-intercept will be k.

Next let us consider different gases of equal mass.

2020 p1 q6 compare different gases of equal mass

A gas with a smaller molar mass will have a greater number of moles.

Since y-intercept k = nRT, larger n means k will also be larger.

This means a gas with smaller molar mass will have larger y-intercept k.

2020 p1 q6 deduce which gas is neon

We can now compare the molar mass of the gases given and determine which graph is neon.

CH4 has the smallest molar mass of 16.0 hence largest n and k that corresponds to graph A.

Ne has the next smallest molar mass of 20.2 hence second largest n and k that corresponds to graph B.

Cl2 has the largest molar mass of 71.0 hence its moles and k will be the smallest and that would correspond to graph D.

Therefore the answer to this question will be option B.

Topic: Gaseous State, Physical Chemistry, A Level Chemistry, Singapore

Back to list of questions for 2020 A Level H2 Chemistry Paper 1.

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