14: Simple Models of Matter Flashcards
Where is thermal energy always transferred?
From regions of higher temperature to regions of lower temperature
A change in temperature shows thermal energy has been [ ]
Transferred
What does a net transfer of thermal energy cause?
A change in temperature
What is specific thermal capacity?
The amount of energy needed to raise the temperature of 1 kg of the substance by 1K
What is the set up to measure specific thermal capacity of a solid?
Put a digital thermometer in a hole in your solid
Surround your solid with insulating material
Put an electric heater in another hole in your solid
What is the set up for liquids, in order to find the specific thermal capacity?
Have a heating coil inside a beaker of your liquid with a digital thermometer in the beaker surrounded by insulating material and an insulating lid
Why is the value you get for specific thermal capacity usually too high in experiments? How can you improve this?
Some of the energy from the heater will get transferred to the air and the container. To minimise this affect, start below and finish above room temperature to cancel out gains and losses. Some energy will also be lost due to resistance in the circuit
Describe the experiment to find specific thermal capacity
Heat the substance with the heater so that its temperature increases by about 10 K
Attach an ammeter and voltmeter to your electric heater. You can then calculate the work done by the heater
If you assume all of the work done by the heat is transferred into thermal energy energy in the solid or liquid, you can then plug your data into E = mcΔθ
What is an ideal gas?
A model, based on a set of assumptions
An ideal gas is a good approximation of a real gas as long as the pressure isn’t too great and the temperature is reasonably high, compared with the gas’s boiling point
What does Boyle’s Law state?
At a constant temperature, the pressure p and the volume V of a gas are inversely proportional
Do ideal gases always obey the three gas laws?
Yes
Describe what difference temperature makes to a line on the pressure volume graph
The higher the temperature of the gas, the further the curve is from the origin
How can you investigate the effects of pressure on volume?
The oil confines a parcel of air in a sealed tube with fixed dimensions. A tyre pump is used to increase the pressure in the tube and the Bourdon gauge records the pressure. As the pressure increases the air will compress on the volume occupied by air in the tube will reduce.
Measure the volume of air when the system is that atmospheric pressure, then gradually increase the pressure, noting down both the pressure and the volume of air. Multiplying them together at any point you should give a constant
What does Charles’ law state?
At constant pressure, the volume of the gas is directly proportional to its absolute temperature
What does the graph of pressure against temperature look like for an ideal gas?
A straight line, intersecting the X axis at -273.15 Celsius, with a positive gradient
Describe the set up for the investigation of the pressure law
Put a flask with a stopper on the top and a beaker of water with a thermometer also in the beaker. The stopper in the top of the flask should be connected by tube to a Bourdon gauge
The volume of the tubing must be much smaller than the volume of the flask.
Make sure as much of the flask is submerged as possible
Describe the investigation of the pressure law
Record the temperature of the water and the pressure on the gauge.
Heat the water for a few minutes then remove the heat source, stir the water to ensure it is at her uniform temperature and allow some time for the heat to be transferred from the water to the air. Record the pressure on the gauge and the temperature, then heat the water again and repeat until the water boils. Repeat your experiment twice more with fresh cold water, taking pressure measurements at the same set of temperatures each time.
Plot your results on a graph of pressure against temperature. Draw a line of best fit.
What else can you find in the investigation of the pressure law?
This experiment also allows you to estimate the value of absolute zero, again by extrapolating your line of best fit until it reaches the x-axis
What equation do you get if you combine all three gas laws?
pV/T = constant
What conditions must be met, for a gas to obey as an ideal gas?
Low-pressure and fairly high temperatures
What is R, in gas equations? k?
R is the gas constant for one mole of gas
k is the gas constant for one gas particle
What are some simplifying assumptions that are used in kinetic theory?
Particles occupy a negligible volume compared with the volume of the container
Collisions between particles themselves or at the walls of the container are perfectly elastic, so no energy is lost.
There are negligible forces between particles, except when they collide.
The gas contains a large number of particles to move rapidly and randomly and that the motion of the particle obeys Newton’s laws
What do you use to model the movement of the gas particle?
Random walk
What does a random walk assume?
Each particle starts in one place, moves N steps in random directions, and ends up somewhere else
