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The Ideal Gas Equation

Most gases obey a simple law known as the ideal gas equation. This describes the relationship between the pressure, volume and temperature of a gas.

The ideal gas equation

The ideal gas equation

  • The ideal gas equation is:
  • Pressure × volume = number of moles × gas constant × temperature
  • PV = nRT
  • This equation can be used to calculate any variable in the equation, as long as you know the other three variables.
    • P, V, n, and T are the variables.
    • R is a constant - its value is always 0.08206.
Importance of units

Importance of units

  • When using the ideal gas law, it is important to make sure you are using only SI units:
  • Pressure must be in atmospheres (atm).
  • Volume must be in liters (L).
  • Temperature must be in Kelvin (K).
  • These units are the scientific standard - they are all related and allow for easily understood numbers.
  • Using different units will give you the wrong answer!
An example

An example

  • The pressure of 1 mole of a gas is 1 atm at a temperature of 298 K. What is its volume?
    • PV = nRT
    • V = nRT ÷ p
    • V = 1 × 0.08206 × 298 K ÷ 1 atm
    • V = 24.8 L

The Kelvin Scale

The Kelvin scale is a temperature scale that is commonly used in science. For the SAT Chemistry Subject Test you need to be able to convert °C to Kelvin.

The Kelvin scale

The Kelvin scale

  • The Kelvin scale is an absolute temperature scale defined to have 0 K at the lowest possible temperature, called absolute zero.
Absolute zero

Absolute zero

  • Absolute zero (0 K) is the lowest possible temperature.
  • At absolute zero, there is no temperature.
    • This means that there is no kinetic energy or vibration of molecules.
Converting from degrees to Kelvin

Converting from degrees to Kelvin

  • To find degrees from Kelvin, just add 273.
    • E.g. 0oC = 273 K.
    • E.g. Water boils at 373 K.
Jump to other topics
1

Structure - Models of the Particulate of Matter

2

Structure - Models of Bonding & Structure

3

Structure - Classification of Matter

3.1

The Periodic Table: Classification of Elements

3.2

Periodic Trends

3.3

Group 1 Alkali Metals

3.4

Halogens

3.5

Noble gases, group 18

3.6

Functional Groups: Classification of Organic

3.7

Functional Group Chemistry

3.8

Alkanes

3.9

Alcohols

3.10

Halogenoalkanes

4

Reactivity - What Drives Chemical Reaction?

5

Reactivity - How Much, How Fast & How Far?

6

Reactivity - The Mechanisms of Chemical Change

7

Measurement, Data Processing & Analysis

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