The experimental gas laws Flashcards
What is the pressure of a gas?
- force per unit area that the gas exerts normally (perpendicular) on the surface
What does the pressure of the gas depends on>?
- temp
- volume of container
- mass of gas
What is an isothermal change?
any change at constant tempertaute
What is Boyle’s law?
- 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
How can Boyle’s law be investigated?
- can be used to show that the gas pressure x its volume is constant
- slow pressure changed
- time allowed to reach thermal equilibrium
What does the pressure-volume graph look like at different temperatures
- higher the temp, the more force exerted on a given area
- at a given volume, pressure is higher when temperature is higher
what is charles’ law?
- 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
How is Charles’ Law investigated? Give an explanation
- 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
What is an isobaric change?
- change at constant pressure
What must happen when work is done to change the volume of gas when pressure is constant?
- energy ,ust be transferred by heating to keep the pressure constant
- work = p ΔV
What is the pressure law?
- P /T constant
How can absolute zero be estimated using Charles’s Law?
- 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
What are the possible reason for calculating a value for abosulute zero in the Charles’s Law experiment?
- 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
if the tube in the boyles law experiment does not have a scale for volume, what is the alternative?
- the tube has a uniform bore
- therefore volume is proportional to length
What are the safety precautions in the Boyle’s law experiment?
- avoid excessive pressure and ensure the connection are secure
- to avoid oil being sprayed at high pressure over observers
- check the function of apparatus
How do you ensure the conditions for Boyle’s law are present?
- 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
In terms of molecular motion, wy does the pressure of the gas vary with absolute temperature?
- average KE increase with temp
- increase collision freq
- change in p greater
- rate of change of p greater
- force/pressure is therefore greater
