Starter What would happen if you kept filling a balloon with gas? What would happen if you put a full sealed balloon of gas into the refrigerator? Why would this happen?

The ideal gas equation Learning outcomes: State the ideal gas equation Use SI units correctly Manipulate the ideal gas equation to calculate the number of moles of a gas at a given volume, temperature and pressure Specification reference

What is an ideal gas? An ideal gas is one which follows this equation: pV=nRT Where: p = pressure in Pa (Nm -2 ) V = volume (in m 3 ) n= number of moles T= temperature (in K) R = gas constant (8.31 JK -1 mol -1 ) No gas is actually ideal... But at room temperature and pressure (RTP) it works pretty well for most.

Really... Where does that equation come from The ideal gas equation is a combination of; Boyle’s law – it states that the product of pressure and volume is a constant so long as the temperature stays constant Charles’ law – it states that volume is proportional to the temperature so long as the pressure is constant Gay-Lussac’s law – it states that pressure is proportional to the temperature as long as the volume remains constant All these equations are in the book – you are not expected to know them

Using the ideal gas equation Key things – you must use the correct units (and convert values if they aren’t correct) To convert °C to Kelvin, add 273 To convert kPa to Pa, multiply by 1000 To convert dm 3 into m 3, divide by 1000 To convert cm 3 into m 3, divide by 10 6

Rearrange... Make: Volume Pressure Temperature Number of moles... the subject of the equation

Answers

Worked example Volume from the ideal gas equation. If a gas has a temperature of 20.0°C, at a pressure of Pa, and n= 1 for one mole of gas, what is the volume? V = nRT/P V = 1 x 8.31 x 293/ V = m 3 Convert to cm 3 by multiplying by 10 6

Question Calculate the volume of 2 moles of gas if the temperature is 30°C, and the pressure is Pa. Calculate the pressure of 0.5 moles of a gas if the volume is cm 3, and the temperature is 25°C. Calculate the volume in m 3 of 2.5x10 -2 moles of oxygen gas at a pressure of 150kPa and a temperature of 50°C

Worked example Finding the number of moles: How many moles of hydrogen molecules are present in a volume of 100cm 3 at a temperature of 20.0°C and a pressure of 100kPa? R = 8.31 JK -1 mol -1 Convert base units 100kPa = Pa 100cm 3 = 100 x °C = 293K n = PV/RT = x 100x10 -6 /8.31 x 293 = moles

Questions Calculate how many moles of hydrogen molecules are present in a volume of cm 3, at Pa and 25°C. State how many moles of carbon dioxide molecules would be present under the same conditions. Explain your answer.

Useful things to calculate If you know the number of moles present in any given mass of gas, you can find the mass of one mole of gas and thus the M r of that gas. Once you have calculated the number of moles, you can rearrange the equation n = m/M r (M r = mass/n) and then find the relative formula mass of that gas.

Homework Complete the activity on kerboodle esources/node/12362/page/1/content/ esources/node/12362/page/1/content/91127 Link also on show my homework Once you have done that, complete the ideal gas questions on the worksheet