P2.2 - thermal properties and temperature

Question 1

What is thermal expansion?

Answer 1

The increase in movement of the particles causes objects to become slightly larger as they are warmed up.
Higher temperatures cause particles to gain energy and move faster & farther apart/increase its thermal energy.

Question 2

What happens to railway lines due to thermal expansion?

Answer 2

The forces produced by a solid material when it expands are very large. A long piece of metal (e.g. railway line) can easily buckle due to the large force. To avoid damage, small air gaps can be left between each length of track to allow for expansion.
Same with bridges.

Question 3

Explain briefly 3 experiments showing thermal expansion in solids

Answer 3

1. Ball and ring - pass a cool ball through the ring, heat it, and see if it still fits
2. Bimetallic strip - a strip made of 2 layers of different metals (brass & steel) is heated over a Bunsen burner. Since brass expands more than steel, the brass layer will be slightly longer, so the strip will bend towards the steel side.
3. Flask of liquid - hold a flask with colorful liquid in your hands and see how the level in the tube rises due your body heat

Question 4

State 2 situations where thermal expansions is useful and 3 where it’s harmful

Answer 4

+ mercury in thermometers, hot air balloons
- buckling of railway tracks; cracks in roads/bridges; pipes bursting

Question 5

What is evaporation?

Answer 5

The change of state from liquid to a gas below the liquid’s boiling point when it is exposed to air. It takes time, as only the fastest particles can escape the intermolecular forces/bonds which hold particles in a liquid close together.

Question 6

What expands most due to heating?

Answer 6

Gas - most due to almost no forces of attraction
Liquid - more movement than in solids, less than in gases
Solid - expansion is very small

Question 7

Differences between the 2 types of vaporisation

Answer 7

Boiling - happens everywhere in a liquid, happens at a specific temperature
Evaporation - happens at the surface where particles break free from bonds. Happens at any temperature below the boiling point
Both gain energy by taking it from the surroundings, causing the surroundings to cool down

Question 8

What is the effect of evaporation on temperature and energy

Answer 8

Since the fastest particles in the liquid escape first, the average speed of the remaining particles decreases during evaporation. This means that the temperature of the remaining liquid decreases, as does the average energy of particles.

Question 9

State and explain 3 factors affecting evaporation

Answer 9

1. Surface area - increasing sa increases the number of particles near the surface and therefore the rate of evaporation
2. Temperature - increasing temperature means that more particles are now moving fast enough to escape/have enough energy to break their bonds, increasing evaporation rate
3. Airflow - removes already saturated air which was slowing down the evaporation rate since the concentration gradient was slow.

Question 10

What happens to the temperature when a substance is changing state?

Answer 10

The temperature does not change because the energy provided causes changes to the bonds between the particles instead of changing their speeds

Question 11

Write a brief lab report on how surface area affects the rate of evaporation of a liquid

Answer 11

Hypothesis: The larger the surface area of the water in contact with the air, the higher the rate of evaporation. This is because larger surface area will result in more particles of the water being able to escape at the same time, since evaporation only occurs at the surface of a liquid
IV: surface area of water in contact with air (cm^2, calculated by the area of the container’s opening, first measuring the diameter: radius^2 x pi)
DV: rate of evaporation (g/hour, mass of liquid evaporated per hour
CVs: type of liquid (water), initial temperature (degrees C, controlled by measuring it before the start of the experiment), initial mass of liquid (g, measured using digital balance.)
Apparatus:
Ruler
Containers with openings of different diameters (5cm, 10cm, 15cm, 20cm and 25cm)
Timer
Digital balance
Water
Thermometer
Clamp stand
Method:
1. Measure the diameter of each container and calculate the area of the opening which is (diameter/2)^2 x pi. Record these values in a table
2. Place the smallest container on a digital balance, and add 20 grams of water (final mass - initial mass of just the container)
3. Record the initial mass
4. Using a clamp stand, clamp the thermometer above the container to measure the temperature and make sure that it is constant throughout the experiment
5. Start a timer for one hour
6. After the one hour has passed, place the container on the digital balance and record the final mass
7. Calculate and record the rate of evaporation by doing initial mass of water & container - final mass of water & container per hour.
8. Repeat steps 2-7 for each of the other 4 containers
Important things to remember:
- Apparatus must be drawn set up as it will be during the experiment (not individual equipment)
- Multiple trials are not needed
- How we get the IV (surface area of liquid in contact with air) should be explained. E.g. measure the diameter, and calculate the area by doing pi x r^2.
- At least 5 different diameters
- Beakers and other apparatus should be 2D