# LC Chem 3 Moles, Gases, and Stoichiometry

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chemistry

### Mole

The amount of a pure substance that contains the same number of particles as there are atoms of carbon-12 in 12g of 12C

### 6 x 10^23

Avogadro's number (number of particles in 1 mole)

### Molar mass

The mass in grams of one mole of the substance.

### Diffusion

The spontaneous movement or spreading out of a substance to fill a space due to the natural movement of its particles

### Temperature

A measure of the degree of hotness of an object

To convert from Celsius to Kelvin

### Kelvin

SI unit of temperature

### 0K

The temperature at which a gas would occupy no volume, if it could be cooled indefinitely without becoming a liquid or a solid

### N/m2

SI unit of pressure (also called the pascal, Pa)

### 100000 Pa

Normal atmospheric pressure in Pa

### 1000 Pa

Number of Pa in 1 kPa = 1,000 Pa.

### m3

SI unit of volume

### 1000 cm3

Number of cm3 in 1 litre

### 1000000 cm3

Number of cm3 in 1 m3

### 1000 L

Number of litres in 1 m3

### 273 K

standard temperature

### 100000 Pa

standard pressure (Pa)

### Boyle's Law

At constant temperature, the volume of a fixed mass of gas is inversely proportional to its pressure.

### Charles' Law

At constant pressure, the volume of a fixed mass of gas is directly proportional to its temperature measured on the Kelvin scale.

### 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 the ratio of small whole numbers provided the volumes are measured at the same temperature and pressure.

### P1V1/T1 = P2V2/T2

Equation for Combined Gas Law

Equal volumes of gases contain equal numbers of molecules, under the same conditions of temperature and pressure.

### Molar volume

The volume occupied by one mole of any gas

### 22.4 L

Molar Volume at s.t.p.

### 24 L

Molar Volume at room temperature and pressure

### Assumptions of the Kinetic theory of Gases

1. Gases are made up of particles that are in continuous motion, colliding with each other and with the walls of the container.
2. There are no attractive or repulsive forces between the molecules of a gas.
3. The volume of the gas molecules is negligible compared with the spaces between them.
4. When molecules collide, the collisions are perfectly elastic.
5. The average kinetic energy of the molecules is proportional to the temperature in Kelvin scale.

### Limitations to the Kinetic theory of Gases

1. There are attractive and repulsive forces between the molecules of a gas.
2. The volume of the molecules is not negligible compared with the space that they occupy.
3. Collisions are not perfectly elastic.

### Ideal gas

One which obeys all the gas laws and under all conditions of temperature and pressure

### Low pressure and High temperature

Conditions at which real gases behave most like an ideal gas

### pV=nRT

Equation of State for an Ideal Gas

### Pa

Units in which P (pressure) is measured in Ideal Gas Equation

### m3

Units in which V (volume) is measured in Ideal Gas Equation

### n

Number of moles of gas present in Ideal Gas Equation

### R

Universal gas constant that converts the units (8.31 J/mol/ K) in Ideal Gas Equation

### K

Units in which T (temperature) is measured in Ideal Gas Equation

### Empirical formula

The formula showing the simplest whole number ratio of the numbers of different atoms present in the molecule

### Molecular formula

The actual number of atoms of each element present = empirical formula x n

### % mass of element

(Atomic mass of element / Molecular mass of compound) x 100

### Limiting reactant

The reactant that determines the amount of product formed

### In excess

The reactants that are left over are said to be ...

### Theoretical yield

The yield of a product that is calculated from the chemical equation.

### Actual yield

The yield that is obtained in practice.

### Percentage yield

(Actual yield / Theoretical yield) x 100

Example: