An assumption used in the ideal gas model is that gas particles have
strong attractive forces between neighbouring particles.
negligible volume compared with the volume of the container.
collisions in which total kinetic energy decreases.
fixed positions except when the container is heated.
A fixed amount of ideal gas is heated in a rigid sealed container. The pressure increases because the particles
expand in size and occupy a greater fraction of the container.
move faster and collide more forcefully with the container walls.
attract one another more strongly at the higher temperature.
collide inelastically and transfer energy to the container walls.
The conditions under which a real gas is expected to behave most like an ideal gas are
high temperature and low pressure.
low temperature and low pressure.
low temperature and high pressure.
high temperature and high pressure.
The volume occupied by of an ideal gas at STP is
A fixed amount of ideal gas occupies at . The gas is heated to at constant pressure. Its final volume is
A gas is collected over water at . The total pressure is and the water vapour pressure is . The pressure to use for the dry gas in is
A sealed container holds a sample of gas that is modelled as ideal.
Outline two assumptions made in the ideal gas model.
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A sample of ethene, , has a volume of at STP. The molar volume of an ideal gas at STP is .
Calculate the amount, in mol, of ethene in the sample.
Calculate the mass of ethene in the sample.
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An ideal gas has a volume of at and . Using , the amount of gas is
Under the same conditions of temperature and pressure, the gas expected to deviate most from ideal behaviour is
The graph shows results from an investigation using a fixed amount of ideal gas at constant temperature.
The relationship shown is best interpreted as

is directly proportional to .
is independent of .
is directly proportional to .
is directly proportional to .
A fixed amount of a real gas is compressed and cooled.
State the conditions under which a real gas deviates most from ideal behaviour.
Explain why these conditions cause greater deviation from ideal behaviour.
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A student investigates the pressure of a fixed amount of gas at constant temperature by changing the volume of the container.

Identify the independent variable in this investigation.
State the relationship between pressure and volume for this gas sample.
Explain, using the particle model, why the pressure changes when the volume is decreased.
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A balloon contains of helium at and . Assume ideal gas behaviour.
Convert the temperature to kelvin.
Calculate the volume of helium in .
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A fixed mass of gas is sealed in a rigid metal cylinder. Its pressure is at . The cylinder is warmed to .
Calculate the final pressure of the gas, assuming ideal behaviour.
State why temperature must be converted to kelvin in this calculation.
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A fixed amount of an ideal gas was kept at constant temperature while the volume of the container was changed. The graph shows the measured pressure at each volume, with one point labelled A.

Describe the relationship shown by the graph.
Use point A to calculate the value of for the gas sample.
Explain, using the particle model, why the pressure increases when the volume is decreased at constant temperature.
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Different gases were measured at standard temperature and pressure, STP. The table shows the amount of gas and the volume occupied by each sample.
| Sample | Amount / mol | Volume / dm^3 |
|---|---|---|
| A | 0.150 | 3.41 |
| B | 0.500 | 11.35 |
| C | 0.750 | 17.0 |
Calculate the molar volume using the data for sample B.
State why the gases have similar molar volumes even though their particles have different masses.
fourth sample contains of an ideal gas at STP. Calculate its volume in .
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A sample of gas occupies at and . Using , the molar mass of the gas is
A fixed amount of ideal gas changes from , and to and . The final pressure is
In an experiment to determine the molar mass of a gas, some gas escapes before its volume is measured. The mass loss of the gas source is measured correctly. The calculated molar mass will be
too high, because the calculated amount of gas is too high.
too low, because the calculated amount of gas is too high.
too high, because the calculated amount of gas is too low.
too low, because the calculated amount of gas is too low.
A volatile liquid is vaporized and the gas is collected over water. The mass of liquid vaporized is . The gas volume is at . The total pressure is and the water vapour pressure at is .
Calculate the pressure of the dry gas.
Determine the molar mass of the volatile liquid.
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An impure sample of calcium carbonate decomposes on heating according to the equation:
A sample produces of at and . Assume ideal gas behaviour.
Calculate the amount, in mol, of produced.
Calculate the percentage by mass of calcium carbonate in the impure sample.
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Ammonia, , and nitrogen, , are compared under the same conditions of and .
Identify which gas is expected to deviate more from ideal behaviour.
Explain your answer in terms of the ideal gas model.
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A rigid vessel of volume contains of argon at . A further of argon is added and the vessel is then heated to . Assume ideal gas behaviour.
Calculate the initial pressure in the vessel.
Calculate the final pressure in the vessel.
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The compressibility factor, , is equal to . For an ideal gas, . The table shows values of for nitrogen at different temperatures and pressures.
| T / K | 1.0 MPa | 5.0 MPa | 10.0 MPa |
|---|---|---|---|
| 200 | 0.98 | 0.88 | 0.76 |
| 300 | 0.99 | 0.94 | 0.86 |
| 400 | 1.00 | 0.98 | 0.95 |
Identify the conditions in the table under which nitrogen shows the greatest deviation from ideal behaviour.
Describe the effect of increasing temperature on the value of at the same pressure.
Explain why real gases deviate more from ideal behaviour under the conditions identified in part (a).
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Oxygen gas was collected in a gas syringe during the decomposition of hydrogen peroxide. The table shows the final gas volume and the conditions in the laboratory.
| Quantity | Value |
|---|---|
| Final oxygen volume / cm^3 | 72.0 |
| Pressure / kPa | 101 |
| Temperature / K | 295 |
Calculate the amount, in mol, of oxygen collected at the end of the experiment.
State one variable, other than amount of gas, that must be measured to use the ideal gas equation for this sample.
Suggest one reason why the calculated amount of oxygen could be lower than the amount actually produced.
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A gas sample in a sealed piston was changed from state 1 to state 2. The diagram gives the pressure, volume and temperature for state 1, and the volume and temperature for state 2.

Calculate the pressure of the gas in state 2.
Explain why temperature values in gas calculations must be in kelvin rather than degrees Celsius.
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A fixed amount of gas was sealed in a rigid container. The pressure was recorded at different temperatures. The graph shows pressure plotted against temperature in degrees Celsius.

Identify the independent variable, the dependent variable and one controlled variable in this investigation.
Use the extrapolated line to estimate the temperature at which the pressure would be zero.
Explain the linear relationship shown by the graph using the ideal gas equation.
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Students used measured values of pressure, volume, amount and temperature for an ideal gas to calculate the gas constant, . The table and plot show their results from several trials.
| Trial | Pressure / kPa | Volume / dm^3 | Amount / mol | Temperature / K |
|---|---|---|---|---|
| A | 99.8 | 0.250 | 0.0100 | 300 |
| B | 100.1 | 0.249 | 0.0100 | 300 |
| C | 99.4 | 0.251 | 0.0100 | 300 |
| D | 120.0 | 0.250 | 0.0100 | 300 |
Calculate for trial A using the data in the table.
Identify the anomalous trial.
Evaluate whether the results support the ideal gas model.
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The graph shows pressure against temperature for a fixed amount of gas in a container of constant volume. The ideal prediction and experimental results for a real gas are shown.

State the relationship predicted by the ideal gas model for this experiment.
Explain why the experimental pressure may be lower than the ideal prediction at lower temperatures.
Suggest why an accurately plotted graph is more useful than a sketch graph for this investigation.
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A student determines the molar volume of hydrogen gas by reacting magnesium with excess hydrochloric acid and collecting the hydrogen in a gas syringe. A strip of magnesium produces of hydrogen at room temperature and pressure.

Calculate the experimental molar volume of hydrogen in .
Suggest one systematic error that would make the calculated molar volume too low.
Suggest one improvement to increase the reliability or validity of the result.
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A gas was collected over water and used to determine the molar mass of a volatile compound. The table shows the experimental data. The total pressure is the pressure of the dry gas plus the pressure of water vapour.
| Quantity | Value | Unit |
|---|---|---|
| Total pressure | 100.8 | kPa |
| Pressure of water vapour | 3.17 | kPa |
| Volume of gas collected | 72.4 | cm^3 |
| Temperature | 298 | K |
| Mass of volatile compound | 0.118 | g |
Determine the pressure of the dry gas.
Calculate the amount, in mol, of dry gas collected.
Calculate the molar mass of the gas and suggest one source of systematic error if the water vapour pressure were not subtracted.
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The table shows compressibility factors for methane, carbon dioxide and ammonia under comparable conditions. An ideal gas has .
| Condition | Methane | Carbon dioxide | Ammonia |
|---|---|---|---|
| 300 K, 5.0 MPa | 0.86 | 0.68 | 0.50 |
| 500 K, 1.0 MPa | 0.98 | 0.94 | 0.89 |
Identify the gas and conditions in the table that are closest to ideal behaviour.
Compare the deviations of carbon dioxide and ammonia at low temperature and high pressure.
Suggest why ammonia deviates more from ideal behaviour than methane under comparable conditions.
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The molar mass of a volatile liquid was determined by vaporizing it in a flask of known volume. The apparatus and data are shown.

Calculate the amount of vapour in the flask, assuming ideal behaviour.
Calculate the molar mass of the volatile liquid.
Suggest one reason why the calculated molar mass would be too high if some liquid remained unevaporated in the flask.
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A fixed amount of gas was compressed at constant temperature. The data were processed by plotting pressure against the reciprocal of volume, . The best-fit line has a gradient shown on the graph.

State the evidence from the graph that pressure is inversely proportional to volume.
Use the gradient of the graph to calculate the amount of gas in the sample at .
Suggest why the data might curve away from the straight line at very small volumes for a real gas.
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A student reacts of magnesium ribbon with excess dilute hydrochloric acid and collects the hydrogen gas in a gas syringe. The collected gas is saturated with water vapour at . The atmospheric pressure is . The vapour pressure of water at this temperature is .

The mass of magnesium used is .
Calculate the amount, in mol, of magnesium used.
Calculate the volume, in , of dry hydrogen expected.
The student actually collects of gas. Evaluate one experimental reason, other than measurement uncertainty in mass, for the lower volume.
Explain why hydrogen is expected to behave nearly ideally under these conditions.
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A fixed amount of gas is placed in a sealed syringe at . The pressure is measured at different volumes.

The pressure is when the volume is .
Calculate the amount of gas in the syringe.
Predict the pressure when the volume is increased to at the same temperature.
Explain, using the particle model, why the pressure decreases when the volume is increased at constant temperature.
Discuss one advantage and one limitation of using the plotted data rather than only a sketch graph for this investigation.
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A sealed metal aerosol can contains a fixed amount of propellant gas. At the gas pressure inside the can is . The can volume is constant.
The can is heated to .
State why the combined gas law can be applied to this change.
Calculate the pressure in the can at .
The can is designed to rupture at . Determine the temperature, in , at which rupture would be expected if the gas behaved ideally.
Explain why using temperature in directly in the combined gas law would give an invalid prediction.
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Helium, carbon dioxide and ammonia are stored separately in identical cylinders at the same temperature and pressure. The cylinders are then cooled and compressed.
Compare the expected deviations from ideal gas behaviour for helium and ammonia under the cooled, compressed conditions.
Identify which gas is expected to deviate more from ideal behaviour.
Explain your answer in terms of the ideal gas model.
Explain why low temperature and high pressure both increase deviation from ideal behaviour.
State one assumption of the ideal gas model that is least valid for carbon dioxide at high pressure.
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A fixed amount of gas in a rigid metal flask was cooled. The graph compares the measured pressure with the pressure predicted by the ideal gas equation.

Using the ideal gas model, calculate the predicted pressure at if the pressure is at .
Compare the measured pressure at with the ideal prediction.
Evaluate the suitability of the ideal gas model for these data.
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A volatile liquid is vaporized in a sealed flask at . After cooling, the mass of condensed liquid in the flask is found to be . The pressure of the vapour before cooling is .

Use the data to determine the molar mass of the volatile liquid.
Calculate the amount, in mol, of vapour in the flask.
Calculate the molar mass of the liquid.
The empirical formula of the liquid is . Determine its molecular formula.
Suggest two improvements to increase the reliability or accuracy of the molar mass determination.
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A sample of impure calcium carbonate is reacted with excess hydrochloric acid. The carbon dioxide produced is collected and measured at and . A sample produces of carbon dioxide.
sample produces of carbon dioxide.
Calculate the amount, in mol, of carbon dioxide produced.
Calculate the percentage by mass of calcium carbonate in the sample.
Calculate the volume of carbon dioxide, in , that would be produced at STP if the sample were pure calcium carbonate.
State one reason why the measured volume in part (a) should not be compared directly with the STP volume in part (b) without calculation.
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A gaseous hydrocarbon is collected over water to determine its molar mass. The mass of gas collected is , the gas volume is , the temperature is and the total pressure is . The vapour pressure of water at is .

Determine the molar mass of the hydrocarbon.
Calculate the pressure of the dry hydrocarbon gas.
Calculate the amount, in mol, of hydrocarbon gas.
Calculate the molar mass of the hydrocarbon.
Evaluate the effect on the calculated molar mass if the vapour pressure of water were not subtracted.
Suggest why the hydrocarbon may still not behave perfectly ideally in this experiment.
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In an experiment, carbon dioxide is generated and collected in a gas syringe at constant temperature. At RTP, one mole of gas occupies . A graph of mass lost by the reaction flask against gas volume is used to determine the molar mass of the gas.

At RTP, where the molar volume of a gas is , the best-fit line shows that of carbon dioxide corresponds to of gas.
Calculate the amount, in mol, in of gas.
Use the value from (a)(i) to calculate the molar mass of the gas.
Explain why a best-fit line is preferable to using one individual data point from the graph.
Suggest one systematic error that would make the calculated molar mass too high.
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Sodium azide, , can decompose rapidly to form sodium and nitrogen gas in an inflator. The simplified equation is:
A sealed test chamber of volume contains nitrogen produced by decomposing of sodium azide. The gas temperature immediately after decomposition is .
sealed test chamber of volume contains nitrogen produced by decomposing of sodium azide. The gas temperature immediately after decomposition is .
Calculate the amount, in mol, of sodium azide decomposed.
Calculate the amount, in mol, of nitrogen gas produced.
Calculate the pressure, in , due to the nitrogen gas.
Discuss two assumptions made when applying the ideal gas equation to the nitrogen immediately after decomposition.
Suggest why the pressure calculated in (a)(iii) may differ from the pressure measured in a real inflator.
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A sample of the mixture decreases to after treatment with excess aqueous potassium hydroxide. Carbon dioxide is removed completely by passing the mixture through excess aqueous potassium hydroxide. All gas volumes are measured at the same temperature and pressure unless stated otherwise.
sample of the mixture decreases to after treatment with potassium hydroxide.
Determine the volume of carbon dioxide in the original mixture.
Determine the mole fraction of carbon dioxide in the original mixture.
State one assumption needed for the volume decrease to represent only carbon dioxide.
The remaining oxygen, volume , is initially at and . It is compressed to and heated to . Calculate the final pressure.
Explain why the calculation in (b) would be less reliable if the oxygen were compressed to a much smaller volume at low temperature.
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The quantity is equal to for an ideal gas. A student measures this quantity for two real gases at as pressure is increased. The plotted values are hypothetical gas-phase data used to illustrate deviation from ideal behaviour.

Use the graph to compare the behaviour of methane and ammonia.
Identify which gas behaves more ideally over the pressure range shown.
Explain the difference in behaviour in terms of intermolecular forces.
Explain why increasing pressure generally increases deviation from ideal gas behaviour.
Evaluate whether a mathematical correction for real gases is required by the ideal gas model in this syllabus context.
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A student uses a computer simulation to investigate a fixed amount of ideal gas. The simulation can hold either pressure, volume or temperature constant while the other variables are changed.

The student wants to test the relationship between pressure and absolute temperature.
Identify the independent, dependent and controlled variables for a valid investigation.
State the expected graphical relationship for an ideal gas.
The student plots pressure against temperature in and obtains a straight line that does not pass through the origin. Evaluate this graph as evidence for the ideal gas model.
Suggest one advantage of using a simulation and one limitation compared with a laboratory experiment using real gases.
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