To calculate the pressure of a gas we cannot use the equation P = F/A 1.Suggest why not? 2.What equation might we use instead? We measure the volume of a gas not its area therefore we would use the following equation instead: P = F/V 3. What units of measurement might we use to measure volume in a.A solid or gas? b. A liquid? We measure the volume of a solid in cm 3 or m 3 whereas we measure the volume of a liquid in ml or l

1/12/15: Learning Objective: What is the relationship between pressure and volume at a constant temperature? Learning Outcomes: Work out the relationship between pressure and volume at a constant temperature Apply this relationship to a variety of different context Explain why this is the case

Copy and complete: If you seal the end of a syringe and press the plunger, the volume of the gas increases/decreases. Therefore the pressure increases/decreases because __________________. Use this clip to help fill in the blanks: How are pressure and volume related?

Copy and complete: If you seal the end of a syringe and press the plunger, the volume of the gas decreases. Therefore the pressure increases because the particles exert more force over a smaller area and therefore pressure increases. Therefore, As the volume doubles the pressure halves/doubles. As the volume halves the pressure halves/doubles. Does this mean the relationship between volume and pressure at a constant temperature is directly or inversely proportional? Prove this one way or the other mathematically. Sketch a graph of what this would look like.

How do you work out the pressure and volume of gases at a constant temperature? The pressure and volume of a given mass of gas at a constant temperature are related by this equation: Pressure (N/m 3 ) x Volume (m 3 ) = Constant Example: You have a large syringe of air. When the pressure is 2x10 5 Pa the volume of the gas is 4x10 -6 m 3. Calculate the volume when the pressure is 5x10 5. Step 1: Calculate the constant for the volume and pressure given. Step 2: Change the subject of the equation to the quantity that you want. i.e. Volume Step 3: Calculate the quantity with the correct unit

Apply this relationship to a variety of different context Answer Q1 on the w/s you have been given Answer Q3 on the w/s you have been given Plot a graph of these results: Remember the golden rules:  Give your graph a title  X axis: suitable scales chosen and labelled with variable and units (independent variable - pressure)  Y axis: suitable scales chosen and label with variable and units (dependent variable - volume)  Plot the points (within 1mm)  Suitable line of best fit drawn Use the graph to estimate the volume of gas produced at a pressure of 500kPa and at 650 kPa Now use the formula you were given earlier to calculate the volume of gas at each pressure. How close was your prediction?

Q: What do you think air pressure is in kPa at sea level? A: About 100,000 Pa or 100kPa or 100,000N/m 3 Q: The volume of air in a crisp packet on the ground is 25cm 3. Calculate the volume of air in a packet of crisps on an aeroplane with a cabin pressure of 80,000 Pa.

Explain why the relationship between pressure and volume of a gas at a constant temperature is inversely proportional The collisions of the gas particles produce a force that is at right angles to the surface. Therefore if you halve the volume, you double the number of collisions (force) between the gas particles and the container, doubling the pressure.