2.1.8 Moles and Gas Volumes

Question 1

What is molar gas volume?

Answer 1

1. Gas volume per mole, units dm^3mol^-1 (decimetres cubed per mole);
2. The volume per mole of gas;
3. At RTP, this value is 24dm^3mol^-1;

Question 2

What is the ideal gas equation? Name the unknowns and the units for these.

Answer 2

pV=nRT
Where:
p - pressure, unit Pa (Pascal)
V - volume m^3; 
n - number of moles
R - the gas constant o f8.314Jmol^-1K^-1: units joule per (K)(mol) - you do not need to remember this value; 
T - temperature, K

Question 3

What is the conversion between m^3 and dm^3?

Answer 3

1m^3=1000dm^3;

Question 4

What is the conversion between k (kelvin) and degrees Celsius?

Answer 4

0 degrees c= 237K;

Question 5

How should one avoid errors with units the ideal gas equation in the exam?

Answer 5

Convert into SI units, before substituting values into the ideal gas equation.

Question 6

What does the Avogadro hypothesis state and why is this important?

Answer 6

1. In, 1811, he put forward a hypothesis that stated at the same conditions of temperature and pressure (the same values as discussed in RTP, at room temp and pressure), any mole of gas would fill the same volume of space;
2. We can compare the no. of molecules in different gasses by comparing their volumes.

Question 7

What is RTP? Link this to the Avogadro hypothesis.

Answer 7

At room temperature and pressure:

1. 1 mole of gas occupies 24dm^3, or 24000cm^3;
2. the volume per mole of gas is 24dm^3/mol;

Question 8

What is the conversion rate between dm^3 and cm^3?

Answer 8

1dm^3= 1000cm^3 (imagine this in a cube, they are cubed values, and 10^3 is 1000, so this is the conversion rate).

Question 9

What is the molar volume of 1 mol of any gas?

Answer 9

The molar volume of any gas at RTP is 24dm^3mol^-1, or 24000cm^3;

Question 10

Why does the Avogadro hypothesis work?

Answer 10

Because the differences in the individual particles have no effect on the overall volume, because the particles are so spread out that any differences become unimportant.

Question 11

Name two methods that chemists would utilise to measure the volume of a gas.

Answer 11

1. Using a gas syringe. The plunger would move out as the gas was collected.
2. (Simpler method) - using a gas delivery tube.

Question 12

What is n?

Answer 12

The amount of gas molecules, in mol.

Question 13

Name the two equations that connect the volume of a gas to n (mol) and molar volume.

Answer 13

Volume is in dm^3;
n=v/24 mol;
Volume is in cm^3;
n=v/24000 mol;

Question 14

How should one convert cm^3 into dm^3?

Answer 14

By dividing it by 1000;

Question 15

Name 5 things that the ideal gas equation assumes.

Answer 15

1. Gasses are in continuous motion - experiencing no IM forces;
2. When they collide with themselves and the walls of the container, they exert pressure;
3. All collisions are elastic - no ke energy is lost;
4. The ke of gas increases with increasing temperature (k);
5. Gasses are so far apart that they can be imagined as identical perfect spheres (any differences in their masses are negligible;

Question 16

What is the Avogadro hypothesis?

Answer 16

1. The number of fundamental particles per mole of substance;
2. This was later determined to be 6.02x10^23mol^-1;

Question 17

What is the process that Avogadro when through to form his hypothesis?

Answer 17

1. An educated guess ;
2. Tested under further investigation;
3. This was rejected due to Dalton’s view of matter only consisting of atoms.
4. Avogadro’s hypothesis was only accepted after his death in 1856, the value of his constant was also later determined.