Charles and Gay-Lussac laws Chemistry p.106 Relationship between - PowerPoint PPT Presentation

Charles’ and Gay-Lussac laws Chemistry p.106

Relationship between  V T Temperature and Volume   V k T (Charles’ Law) V  The volume of an k T enclosed gas is directly proportional to its kelvin V V  temperature, provided 1 2 T T the pressure is kept 1 2 constant.

Typical graph of V versus T V (cm 3 ) T (in K)

Relationship between Temperature and  p T Pressure (Gay-Lussac)   p k T p  k T p p  1 2 T T 1 2

Typical graph of p versus T p kPa T(in K)

Kelvin - Celsius According to the graph the zero point of temperature should be where the gas exerts no pressure, which is impossible. A new Kelvin scale was developed for scientific purposes. 273 K = 0 0 C T (Kelvin) = t (Celsius) + 273

Standard Temperature & Pressure T = 273K p = 101,3 kPa (p = 1,013 x 10 5 Pa)

Example The tyre of a car is pumped to a pressure of 180 kPa at a temperature of 17 0 C. Due to the friction with the surface of the road the temperature rises to 37 0 C. Assume that the volume of the tyre remains constant and then calculate the pressure of the air in the tyre. p p  1 2 T T 1 2 180 p  2 290 310  p 192 kPa 2

Use the formula like this: =

Homework Exercise 3 p. 111, no. 2, 4.1, 4.3, 5.1 Exercise 4 p. 119, no. 6, 9

Graph of V versus T 2.1 V (cm 3 ) Draw a straight line graph of volume versus temperature. Choose an appropriate scale for the axes given below. Stipulate the points. Supply 100 your graph with an appropriate heading. 80 60 40 20 -240 -180 -120 -60 T ( o C) 60 120

Graph of V versus T 2.2 Extrapolate (extend) your graph and determine at which temperature the V (cm 3 ) graph will intercept the temperature axis. - 273 o C 100 80 60 40 20 -240 -180 -120 -60 T ( o C) 60 120

Graph of V versus T 2.3 Write down in words the relationship between the pressure and Kelvin V (cm 3 ) temperature. Pressure is 100 directly 80 proportional to the temperature 60 in kelvin if the 40 volume remains 20 constant. -240 -180 -120 -60 T ( o C) 60 120

Graph of V versus T 2.4 From your graph, determine the volume at 173 K. Show on the graph V (cm 3 ) how you obtained this value 44 cm 3 100 80 60 40 20 -240 -180 -120 -60 T ( o C) 60 120

Graph of V versus T 2.5 How will the gradient of the graph be affected if a larger mass of gas is used? V (cm 3 ) Write down ONLY increase, decrease or stays the same. 100 Increase, 80 if the pressure remains 60 constant 40 20 -240 -180 -120 -60 T ( o C) 60 120

4.1 A gas occupies 250 cm 3 at 100 kPa and 40 o C. Calculate the volume which the gas will occupy at the following temperature, if the pressure is kept constant: 100 o C cm 3 V 2 =

4.3 A gas occupies 250 cm 3 at 100 kPa and 40 o C. Calculate the volume which the gas will occupy at the following temperature, if the pressure is kept constant: -150 o C cm 3 V 2 =

5.1 A 32,3 dm 3 sample of gas at 35 o C and 1,2 atmospheric pressure is cooled at a constant pressure until the volume is 28,4 dm 3 . What will the temperature of the gas be now? T 2 = K = - 2,19 o C

6.1 A tyre is filled with air until the pressure gauge reads 220 kPa, before it undertakes a long trip. This gauge shows the pressure in excess of atmospheric pressure (i.e. meter pressure = true pressure - atmospheric pressure). The temperature is then 25 o C. After being driven for a while, the tyre temperature is 70 o C. If it is assumed that the volume of the tyre remains unchanged, what will be the reading on the pressure gauge if it is connected to the tyre at the new temperature of 70 o C? (Hint: Use actual pressure in your calculations.) Initial pressure = 220 + 101,3 = 321,3 kPa p 2 = kPa Meter pressure = 369,8 - 101,3 = 268,5 kPa

6.2 A pressure cooker with a fixed volume contains only water vapour at a pressure of 100 kPa and a temperature of 100 o C. The lid of the pressure cooker is closed, so that no water vapour can escape. The temperature of the water vapour is increased to 120 o C. Calculate the pressure in the pressure cooker at 120 o C. kPa p 2 =

9. A learner makes use of the apparatus set up in the diagram below to test the following hypothesis: "The pressure of a gas is directly proportional to the temperature”. 9.1 What must the learner change to test the hypothesis and how can it be done? Change the temperature and measure the pressure. Heat the water to increase the pressure.

9. A learner makes use of the apparatus set up in the diagram below to test the following hypothesis: "The pressure of a gas is directly proportional to the temperature”. 9.2 Which variables must be kept constant and how is this done? Volume, amount of gas in the flask and the type of gas. Completely seal the flask.

9. A learner makes use of the apparatus set up in the diagram below to test the following hypothesis: "The pressure of a gas is directly proportional to the temperature”. 9.3 Which readings must be taken? Temperature in o C, and pressure

9. A learner makes use of the apparatus set up in the diagram below to test the following hypothesis: "The pressure of a gas is directly proportional to the temperature”. 9.4 Rewrite the hypothesis given in a more correct manner. If the pressure of a gas increases while the volume is kept constant, the temperature will also increase.

9. The learner draws a graph AB of the results p (kPa) and uses the graph to show how the relationship between the pressure and the temperature of A the gas can be deduced. 620 9.5 What is point S on the temperature axis X B called? Absolute zero S -100 -300 -200 100 T ( o C)

9. The learner draws a graph AB of the results p (kPa) and uses the graph to show how the relationship between the pressure and the temperature of A the gas can be deduced. 620 9.6 What is the theoretical pressure of any X B gas at S? 0 kPa S -100 -300 -200 100 T ( o C)

9. The learner draws a graph AB of the results p (kPa) and uses the graph to show how the relationship between the pressure and the temperature of A the gas can be deduced. 620 9.7 Which temperature in o C is represented X B by S for pressure versus temperature in Kelvin? -273 o C S -100 -300 -200 100 T ( o C)

9. The learner draws a graph AB of the results p (kPa) and uses the graph to show how the relationship between the pressure and the temperature of A the gas can be deduced. 620 9.8 Calculate the value of X, the point of X B intercept on the pressure axis. S -100 -300 -200 100 T ( o C) p 1 = 453,78 kPa