The experimental gas laws

Question 1

What is the pressure of a gas?

Answer 1

• force per unit area that the gas exerts normally (perpendicular) on the surface

Question 2

What does the pressure of the gas depends on>?

Answer 2

• temp
• volume of container
• mass of gas

Question 3

What is an isothermal change?

Answer 3

any change at constant tempertaute

Question 4

What is Boyle’s law?

Answer 4

• fixed mass of gas
• constant temp
• pV = constant
• pressue of a fixed mass of gas is inversely proportional to its voluime, provided that temp is kept constant

Question 5

How can Boyle’s law be investigated?

Answer 5

• can be used to show that the gas pressure x its volume is constant
• slow pressure changed
• time allowed to reach thermal equilibrium

Question 6

What does the pressure-volume graph look like at different temperatures

Answer 6

• higher the temp, the more force exerted on a given area
  
  • at a given volume, pressure is higher when temperature is higher

Question 7

what is charles’ law?

Answer 7

• V / T = constant
• constant pressure
• Charles’s Law states that, at constant pressure, the volume of a fixed mass of an ideal gas is directly proportional to its abolute pressure

Question 8

How is Charles’ Law investigated? Give an explanation

Answer 8

• heated water bath
  
  • ice cubes can be used to cool below room temp to give a greater range of readings
• use a gas syringe
• measure volume at certain temp
  
  • ensure the bulb of the thermometer is submerged in the water
• gas decreases in volume as temperature decrease, therefore the syringe is moved

Question 9

What is an isobaric change?

Answer 9

• change at constant pressure

Question 10

What must happen when work is done to change the volume of gas when pressure is constant?

Answer 10

• energy ,ust be transferred by heating to keep the pressure constant
• work = p ΔV

Question 11

What is the pressure law?

Answer 11

• P /T constant

Question 12

How can absolute zero be estimated using Charles’s Law?

Answer 12

• if Kelvin scale used, the plotted graph will be a straight line through the origin
• at 0K volume is zero
• use celcius scale and extrapolate the graph
• till volume is zero this is the vlaue of absoluite zero

Question 13

What are the possible reason for calculating a value for abosulute zero in the Charles’s Law experiment?

Answer 13

• air in syringe did not have time to come to thermal equilibrium with the water bath
  
  • and so the temp of the trapped air was different from the temperature recorded from the thermometer
• friction between the plunger and the wall of the syringe,
  
  • which makes it harder for the air inside to expand
• leak in stopper
  
  • mass of air decreasing
• graph requires a large extrapolation
  
  • making it difficult to determine an accurate value of the intercept

Question 14

if the tube in the boyles law experiment does not have a scale for volume, what is the alternative?

Answer 14

• the tube has a uniform bore
• therefore volume is proportional to length

Question 15

What are the safety precautions in the Boyle’s law experiment?

Answer 15

• avoid excessive pressure and ensure the connection are secure
  
  • to avoid oil being sprayed at high pressure over observers
• check the function of apparatus

Question 16

How do you ensure the conditions for Boyle’s law are present?

Answer 16

• air in tube or syringe must not leak out so that its mass will remain constant
• the changes in pressure should be made slowly, and time for thermal equilibrium to be reached so that the temp of air remains constant

Question 17

In terms of molecular motion, wy does the pressure of the gas vary with absolute temperature?

Answer 17

• average KE increase with temp
• increase collision freq
• change in p greater
• rate of change of p greater
• force/pressure is therefore greater