Chemistry, Third edition

REVISION QUESTIONS 169

Table 10.3Critical temperatures and pressures for common gases

Gas Normal boiling Critical Critical
point/°C temperature/°C pressure/atm

Ammonia  33 132 112
Carbon dioxide 78 (sublimes) 31 73
Ethanol 78 243 63
Hydrogen  252  240 13
Oxygen  183  119 50
Nitrogen  196  147 34
Water 100 374 218

10.1.Convert:

(i) 0.124 torr to standard atmospheres

(ii)exactly 1.5 atm to pascals

(iii)89 kPa to newtons per square metre (N m^2 )

(iv)101.325 kPa to bar

(v) 100 C to kelvin.

10.2.In an experiment (in which all gases were at the same

temperature and pressure before and after reaction) it was

found that 1.21 dm^3 of hydrogen gas reacted completely with

1.21 dm^3 of chlorine gas to produce 2.42 dm^3 of hydrogen

chloride. Using Avogadro’s law, explain whether or not these

volumes confirm the equation

H 2 (g)Cl 2 (g)2HCl(g)

10.3.Potassium chlorate decomposes upon heating in the

presence of a catalyst to give oxygen gas:

2KClO 3 (s)2KCl(s)3O 2 (g)

Calculate the volume of oxygen gas made at room temperature

and pressure (20 °C and 1 atm) when 10.0 g of chlorate is com-

pletely decomposed.

10.4.25.0 kPa of chlorine gas is fed into a previously evacu-

ated cell with a volume of 0.0100 m^3. Oxygen gas was then

added to the cell so that its partial pressure was 50.0 kPa. The

cell temperature is exactly 20C. Calculate:

(i)the total pressure of gas in the cell in pascals

(ii)the mole fraction of oxygen gas in the gas mixture, where

number of moles of O 2

mole fraction of O 2 total number of moles of gas

10.5.A metal can of volume 2000.0 cm^3 contains 2.0 g of

nitrogen gas and 6.0 g of hydrogen gas at exactly 200C. What

is the total pressure of gas in the can?

10.6.A flexible leak-proof balloon of volume 1.00 m^3 was

filled with helium to a pressure of 1.00  105 Pa (N m^2 ) at

293 K. When allowed to ascend to an altitude where the helium

pressure was 5.00  104 Pa, the balloon volume had increased

to 1.66 m^3. Use the ideal gas equation to calculate the number

of moles of He in the balloon at 293 K. Then calculate the

atmospheric temperature at the new altitude.

10.7.Experiments show that the molar volumes of hydrogen,

carbon dioxide and ammonia at 1 atm pressure and 273 K are

H 2 22.4 dm^3 , CO 2 22.3 dm^3 , NH 3 22.1 dm^3. What do these val-

ues suggest about the degree to which these gases deviate from

the ideal gas equation? Explain the trend. (Start this problem

by calculating the molar volume of an ideal gas under these

conditions.)

10.8.A stoppered 2.0 dm^3 flask was half-filled with water at

exactly 40C. Calculate the number of water molecules in the

water vapour. (The saturated vapour pressure of water at 40C

is 7370 Pa.)

10.9.Why do solvents with high vapour pressures at room

temperature usually possess low flash points?

Revision questions

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