Chapter 10 - Properties of Gases Flashcards
Gas
A substance that has no well-defined boundaries but diffuses rapidly to fill ant container in which it is placed
Temperature
The measure of how hot or cold an object is
What are the two scales used to measure temperature?
Celsius °C
Kelvin K
What are the fixed points on the Celsius scale?
0°C and 100°C
What is the fixed point on the Kelvin scale?
0K (absolute 0, i.e when a gas would occupy no volume
State absolute 0 in Celsius and Kelvins
-273°C
0K
State the freezing point of water in Celsius and Kelvins
0°C
273K
State the boiling point of water in Celsius and Kelvins
100°C
373K
Pressure (gas definition)
The force exerted by the gas on a unit area of its container
What is the unit for pressure?
newtons per meter squared (N m⁻²)
a.k.a the Pascal (Pa)
(Pa is a very small unit so kilopascal (kPa) us also used)
1 kPa = ….Pa
1 kPa = 1000 Pa
What is normal atmospheric pressure?
1 x 10⁵ N m⁻² = 1 x 10⁵ Pa = 100 kPa
How do you know the volume of a gas?
The volume of a gas is the same as the container it is held in
What is the SI unit for volume?
cubic meter (m³)
What other units do we use for volume?
cubic centimeters (cm³) liters (L) cubic decimeters (dm³)
1 liter = 1000cm³ = 1dm³
What must we know in order to compare gases?
- temperature and pressure of the gas
- must be measured at the same temperature and pressure as each other
What is standard temperature?
273K or 0°C (freezing point of water)
What is standard pressure?
1 x 10⁵ Pa = 100 kPa
Boyle’s Law
At a constant temperature, the volume of a fixed mass of gas is inversely proportional to its pressure
V ∝ 1/p
pV = k
Explain the outcome of Boyle’s Law
When the volume of the container is decreased, the molecules of gas are moving in a smaller space and so will collide with each other more frequently, causing an increase in pressure
Charles’ Law
At a constant pressure, the volume of a fixed mass of gas is directly proportional to its temperature measured on the Kelvin scale
V ∝ T (kelvin)
V/T = k
Explain the outcome of Charles’ Law
As the molecules heat up, they have more kinetic energy to move around. They collide with each other and the container more frequently and, so as not to have an increase in pressure, the volume increases
Combined Gas Law / General Gas Law
p₁V₁ p₂V₂
——- = ——–
T₁ T₂
When is the Combined Gas Law / General Gas Law used?
In conversions of a gas from one set of conditions to another
Gay-Lussac’s Law of Combining Volumes
In a reaction between gases, the volumes of the reacting gases and the volumes of any gaseous products are in ratios of small whole numbers, provided that the volumes are measured at s.t.p
Avogadro’s Law
Equal volumes of gases contain equal numbers of molecules under the same conditions of temperature and pressure
What is the consequence of Avogadro’s Law?
One mole of gas must have the same volume as one mole of any other gas, under the same conditions
Molar volume
The volume occupied by one mole of a gas
What is the volume of one mole of gas at s.t.p?
22.4L
What is the volume of one mole of gas at room temperature?
24L
Brownian Motion
The random movement of tiny particles suspended in a liquid or gas
Volatile liquid
One with a low boiling point
What are the possible points of error in the experiment to measure the relative molecular mass of a volatile liquid using a conical flask?
○ The lab balance is only accurate to one or two decimal placed
○ The graduated cylinder is not as accurate at measuring volume (as, say, a burette)
○ It is very difficult to cover the entire flask with the water. so the vapor may not be exactly the same temperature as the water
○ The outside of the flask may not be completely dry before reweighing
What are the assumptions of the Kinetic Theory of Gases?
✔1. Gases consist of small particles in continuous motion
✘2. There are no attractive or repulsive forces between molecules of a gas
✘3. Gas molecules are so small that the actual volume is negligible compared with the space they occupy
?4. Collisions between molecules of a gas are perfectly elastic i.e there is no loss of kinetic energy
✔5. The kinetic energy of molecules in a gas is proportional to temperature measured on the kelvin scale
Ideal gas
One that perfectly obeys all the assumptions of the Kinetic Theory of Gases under all conditions of temperature and pressure
When do gases come closest to ideal gas behavior?
At low pressure and high temperature, when the particles are well separated
Real gases
Real gases differ from ideal gases because:
i) forces of attraction do exist between molecules
ii) the volume of the molecules is not negligible
What does the combination of Boyle’s, Charles’ and Avogadro’s Laws give?
Equation of State for an Ideal Gas
pV = nRT
