Thermal Properties & Temperature

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Notes

Thermal Expansion

When a material is heated at constant pressure, its **temperature increases**, **volume expands**, and **density decreases**.
Expansion occurs because molecules gain kinetic energy, vibrate/move faster, and push each other apart.
**Solids expand the least**, **gases expand the most**, and **liquids** are in between.
Useful applications: **liquid-in-glass thermometers** (liquid expands in capillary tube) and **bimetallic strips** (two metals expand at different rates, bending to close a circuit).
Undesirable consequences: **buckling** of railway tracks, road surfaces, and bridges; gaps are built in to allow expansion.

Specific Heat Capacity

**Internal energy** is the total energy stored in a system due to particle motion (kinetic) and positions (potential).
Temperature is a measure of the **average kinetic energy** of particles.
**Specific heat capacity (c)** is the energy required to raise the temperature of 1 kg of a substance by 1 °C.
Low c → heats up/cools down quickly; high c → heats up/cools down slowly.
Equation: \Delta E = m c \Delta \θ , where \Delta E in J, m in kg, c in J/kg°C, \Delta \θ in °C.

Investigating Specific Heat Capacity

Aim: determine specific heat capacity by measuring energy supplied (E = IVt) and temperature change.
Independent variable: **time**; dependent variable: **temperature**; control: material, current, voltage.
Equipment: thermometer, immersion heater, beaker/block, ammeter, voltmeter, power supply, digital balance, stopwatch.
Method: record mass, initial temperature, then heat while recording current, voltage, and temperature every 60 s for 10 min.
Calculate \Delta E = IV\Delta t and c = \Delta E / (m \Delta \θ).
Systematic errors: zero balance, account for evaporation; random errors: stir water, be consistent with fluctuating readings.

Melting & Boiling

Fixed points of pure water: **melting point = 0 °C**, **boiling point = 100 °C** at atmospheric pressure.
During a change of state (melting/boiling), **temperature remains constant** even though energy is still being transferred.
Energy goes into **overcoming intermolecular forces** (potential energy), not increasing kinetic energy.
**Boiling** occurs at the boiling point throughout the liquid; **melting** occurs at the melting point as solid becomes liquid.
**Condensation** (gas→liquid) and **solidification** (liquid→solid) also occur at constant temperature as energy is removed.

Evaporation

Evaporation is a change from **liquid to gas** that occurs **at any temperature** and **only from the surface**.
More energetic molecules near the surface escape, reducing the average kinetic energy → **liquid cools**.
Rate of evaporation increases with: **higher temperature**, **larger surface area**, and **greater air movement**.
Evaporation vs boiling: evaporation at any temperature, only at surface; boiling at boiling point, throughout liquid.

Particle arrangement in solids, liquids, and gases showing relative spacing and motion.

Practice questions

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1.What are the upper and lower fixed points on a Celsius scale thermometer?
Easy
- AThe boiling point of pure water and the freezing point of pure water
- BThe boiling point of saturated salt solution and the freezing point of salt-water
- CThe normal temperature of the human body and the freezing point of salt-water
- DThe boiling point of pure water and absolute zero
2.A substance is cooled. The graph below shows how its temperature changes over time. What is happening in the portion of the graph between X and Y?
Easy
- AThe gas is cooling.
- BThe liquid is freezing.
- CThe gas is condensing.
- DThe liquid is cooling.
3.Which statement best describes a metal experiencing thermal expansion?
Easy
- AThe molecules increase in size.
- BThe molecules vibrate more and move further apart.
- CThe molecules expand and become larger.
- DThe molecules decrease in density.
4.When a substance is melting, what happens to its temperature and internal energy?
Medium
- ATemperature increases, internal energy increases.
- BTemperature remains constant, internal energy increases.
- CTemperature remains constant, internal energy decreases.
- DTemperature increases, internal energy remains constant.
5.Which of the following is a correct unit for specific heat capacity?
Medium
- AJ / kg
- BJ / °C
- CJ / (kg °C)
- DJ kg °C
6.The specific heat capacity of water is 4200 J/(kg °C). How much energy is required to raise the temperature of 2.0 kg of water by 5.0 °C?
Medium
- A42000 J
- B21000 J
- C8400 J
- D16800 J
7.In an experiment to determine the specific heat capacity of a metal block, a student uses an immersion heater. Which of the following is the correct equation to calculate the energy supplied to the block?
Hard
- AE = IVt
- BE = IRt
- CE = V/It
- DE = I²Vt
8.A student investigates the cooling of water. The results show that the rate of cooling is greater when the water is hotter. Which statement explains this?
Hard
- AHotter water has a higher specific heat capacity.
- BHotter water evaporates more quickly, removing more thermal energy.
- CHotter water expands, increasing its surface area.
- DHotter water has a lower density, so it rises and cools faster.

More questions

9.Which of the following factors increases the rate of evaporation of a liquid?
Medium
- ADecreasing the temperature of the liquid
- BDecreasing the surface area of the liquid
- CIncreasing the movement of air above the liquid
- DIncreasing the humidity of the air above the liquid
10.Which of the following is a difference between boiling and evaporation?
Medium
- ABoiling occurs at any temperature, evaporation only at the boiling point.
- BBoiling occurs throughout the liquid, evaporation only at the surface.
- CBoiling is a change from liquid to gas, evaporation is from solid to gas.
- DBoiling requires energy, evaporation does not.
11.Which state of matter expands the most when heated at constant pressure?
Easy
- ASolid
- BLiquid
- CGas
- DAll expand equally
12.A student measures the temperature of water as it is heated. The temperature rises steadily until it reaches 100°C, then remains constant even though heating continues. Which statement explains the constant temperature?
Hard
- AThe water is losing heat to the surroundings at the same rate as it is being heated.
- BThe energy supplied is being used to increase the kinetic energy of the water molecules.
- CThe energy supplied is being used to overcome intermolecular forces during boiling.
- DThe specific heat capacity of water becomes infinite at 100°C.
13.A student investigates how the rate of cooling of water depends on the uncovered surface area. She uses two lids: lid A leaves half the surface uncovered, lid B leaves a quarter uncovered. The temperature readings are shown in the table. Which lid gives a greater rate of cooling?
Medium
- ALid A, because the temperature drops more quickly
- BLid B, because the temperature drops more quickly
- CLid A, because the temperature drops more slowly
- DLid B, because the temperature drops more slowly
14.In an experiment to determine the specific heat capacity of a metal block, a student uses an immersion heater. The energy supplied to the block is calculated using the equation E = IVt. Which additional measurements are needed to calculate the specific heat capacity?
Medium
- AMass of the block and temperature change
- BMass of the block and initial temperature
- CVolume of the block and temperature change
- DDensity of the block and initial temperature
15.A student cools water from 70 °C and records temperature every 30 seconds. The results show that the temperature difference between the water and the room decreases over time. Which statement best explains why the rate of cooling decreases?
Hard
- AThe temperature difference between the water and the surroundings decreases
- BThe water evaporates more quickly as it cools
- CThe specific heat capacity of water increases as it cools
- DThe thermometer becomes less accurate at lower temperatures
16.The fixed points on a Celsius thermometer are based on the properties of pure water. What are these fixed points?
Easy
- AThe melting point of ice and the boiling point of water
- BThe freezing point of salt water and the boiling point of water
- CAbsolute zero and the boiling point of water
- DThe melting point of ice and the normal human body temperature
17.A substance is heated at a constant rate. The graph shows how its temperature changes with time. Between which points is the substance partly solid and partly liquid?
Medium
- ABetween W and X
- BBetween X and Y
- CBetween Y and Z
- DBetween V and W
18.Which statement correctly describes what happens to the particles in a solid when it is heated at constant pressure?
Easy
- AThe particles vibrate more and move further apart
- BThe particles expand
- CThe particles increase in size
- DThe particles move faster and get closer together
19.In an experiment to measure the specific heat capacity of water, a student uses an immersion heater and records the temperature every 60 seconds. The student notices that the temperature does not rise immediately when the heater is switched on. What is the most likely reason?
Hard
- ASome energy is used to heat the immersion heater itself
- BThe water is evaporating
- CThe thermometer has a slow response time
- DThe power supply is fluctuating
20.A student investigates the cooling of water in a metal can. The temperature readings are shown in the table. At t = 0 s, θ = 84 °C; at t = 60 s, θ = 75 °C. What is the average rate of cooling between t = 0 and t = 60 s?
Medium
- A0.15 °C/s
- B9.0 °C/s
- C0.15 °C/min
- D9.0 °C/min
21.A student states that most of the thermal energy lost by hot water in a can is by evaporation, while another student says it is by conduction through the sides. Which addition to the apparatus would best test the role of evaporation?
Hard
- APlace a lid on the can to prevent evaporation
- BWrap the can in insulation to reduce conduction
- CUse a fan to increase air movement over the surface
- DStir the water to ensure uniform temperature
22.A student plots a graph of temperature against time for cooling water. He wants to check if the rate of cooling is proportional to the temperature difference between the water and the room. What shape of graph would indicate direct proportionality?
Medium
- AA straight line through the origin when plotting cooling rate against temperature difference
- BA curve that flattens over time
- CA straight line with a negative intercept
- DA horizontal line
23.A student investigates the cooling of water and records the temperature every 30 seconds. He notices that the temperature readings are sometimes fluctuating. Which precaution would improve the accuracy of the temperature readings?
Hard
- AStir the water before taking each reading
- BUse a larger beaker
- CTake readings more frequently
- DUse a thermometer with a larger range
24.A student measures the volume of water in a measuring cylinder. To obtain an accurate reading, which precaution should be taken?
Medium
- ARead the bottom of the meniscus at eye level
- BRead the top of the meniscus at eye level
- CEstimate to the nearest 10 cm³
- DPour the water into a beaker to read the volume
25.In an experiment to measure the specific heat capacity of a metal block, a student uses an immersion heater. The student records the voltage across the heater as 12.0 V and the current as 2.5 A. The heater is switched on for 300 s. What is the energy supplied to the block?
Medium
- A9000 J
- B900 J
- C90 J
- D9000 W
26.A student investigates the cooling of water. The temperature of the water is recorded every 30 s. The results show that the rate of cooling decreases as the water temperature approaches room temperature. Which statement best explains this observation?
Hard
- AThe rate of heat loss is proportional to the temperature difference between the water and the surroundings.
- BThe specific heat capacity of water increases as it cools.
- CEvaporation stops when the water is close to room temperature.
- DThe thermometer becomes less sensitive at lower temperatures.
27.In an experiment to determine the specific heat capacity of a metal block, the following measurements are taken: mass of block = 0.50 kg, initial temperature = 20.0 °C, final temperature = 30.0 °C, energy supplied = 2000 J. What is the specific heat capacity of the metal?
Medium
- A400 J/(kg °C)
- B100 J/(kg °C)
- C40 J/(kg °C)
- D4000 J/(kg °C)
28.Which of the following is a correct precaution when reading the volume of water in a measuring cylinder?
Easy
- ARead the bottom of the meniscus at eye level.
- BRead the top of the meniscus at eye level.
- CRead the scale from above the measuring cylinder.
- DEstimate the volume to the nearest 10 cm³.
29.A student investigates the cooling of water. The temperature readings are: t=0 s, θ=84 °C; t=60 s, θ=75 °C; t=120 s, θ=70 °C; t=180 s, θ=67 °C. Which statement about the rate of cooling is correct?
Hard
- AThe rate of cooling is greater between 0 and 60 s than between 120 and 180 s.
- BThe rate of cooling is constant throughout the experiment.
- CThe rate of cooling is greater between 120 and 180 s than between 0 and 60 s.
- DThe rate of cooling is zero between 120 and 180 s.
30.In the specific heat capacity experiment, why is it important to stir the water continuously while heating?
Medium
- ATo ensure the temperature is uniform throughout the water.
- BTo increase the rate of heat transfer from the heater.
- CTo prevent the water from boiling.
- DTo reduce heat loss to the surroundings.
31.A student uses an immersion heater to heat a metal block. The power of the heater is 50 W. The block has a mass of 1.0 kg and specific heat capacity 500 J/(kg °C). How long will it take to raise the temperature of the block by 20 °C?
Hard
- A200 s
- B20 s
- C100 s
- D400 s
32.In the cooling experiment with lids A and B, lid A leaves half the surface uncovered, lid B leaves a quarter uncovered. The results show that the water cools faster with lid A. Which conclusion is supported?
Medium
- AA larger uncovered surface area increases the rate of cooling.
- BA smaller uncovered surface area increases the rate of cooling.
- CThe rate of cooling is independent of uncovered surface area.
- DLid B is a better insulator than lid A.
33.Which of the following is a controlled variable in an experiment to measure the specific heat capacity of water using an immersion heater?
Easy
- AThe potential difference across the heater.
- BThe temperature of the water.
- CThe time the heater is switched on.
- DThe mass of the water.
34.A student suggests that the rate of cooling of water is directly proportional to the percentage of uncovered surface area. How would the graph of cooling rate against percentage uncovered area show direct proportionality?
Medium
- AA straight line through the origin.
- BA straight line not through the origin.
- CA curve that flattens off.
- DA horizontal straight line.
35.In the investigation of specific heat capacity, the student uses a digital balance to measure the mass of the water. The balance has a resolution of 0.1 g. Which mass reading is recorded to the appropriate precision?
Hard
- A250.0 g
- B250 g
- C250.00 g
- D250.1 g
36.A student repeats the cooling experiment but uses a metal can instead of a glass beaker. The results show a faster rate of cooling. Which statement explains this?
Medium
- AMetal is a better conductor of heat than glass, so more heat is lost through the sides.
- BMetal has a lower specific heat capacity than glass, so it heats up faster.
- CMetal expands more than glass, increasing the surface area.
- DMetal reflects heat back into the water, reducing heat loss.
37.In an experiment to measure the specific heat capacity of a metal block, a student uses an immersion heater. The student records the voltage across the heater as 12.0 V and the current as 2.5 A. The heater is switched on for 5 minutes. What is the energy supplied to the block?
Medium
- A9000 J
- B150 J
- C1500 J
- D900 J
38.A student investigates the cooling of water in a beaker. The temperature of the water is recorded every 30 seconds. The results show that the temperature difference between the water and the room decreases by half every 30 seconds. If the initial temperature difference is 40 °C, what is the temperature difference after 90 seconds?
Hard
- A5 °C
- B10 °C
- C20 °C
- D2.5 °C
39.A student uses an immersion heater to heat 0.5 kg of water. The heater supplies 2100 J of energy, and the temperature of the water rises from 20 °C to 21 °C. What is the specific heat capacity of water?
Medium
- A4200 J/(kg °C)
- B2100 J/(kg °C)
- C8400 J/(kg °C)
- D1050 J/(kg °C)
40.The graph shows temperature against time for a substance being heated at a constant rate. Which section of the graph shows the substance undergoing condensation?
Hard
- AA horizontal section at a lower temperature
- BA horizontal section at a higher temperature
- CA sloping section with positive gradient
- DA sloping section with negative gradient

Slides

Thermal Expansion

When a material is heated at constant pressure, its temperature increases, its volume increases (expands), and its density decreases.
This happens because molecules vibrate or move faster, colliding more often and pushing each other apart.
Solids expand the least, gases expand the most, and liquids are in between.

When a solid is heated, what happens to the molecules?

The molecules expand.
The molecules vibrate more and move apart.
The molecules become smaller.
The molecules stop moving.

Uses and Consequences of Thermal Expansion

Useful applications: liquid-in-glass thermometers (liquid expands in a capillary tube) and temperature-activated switches (bimetallic strip bends when heated).
Undesirable consequences: metal railway tracks, road surfaces, and bridges can buckle if they expand too much.
Gaps are built into structures to allow for expansion without damage.

Which of these are true about thermal expansion?

Liquid-in-glass thermometers rely on the expansion of a liquid.
A bimetallic strip consists of two metals that expand at the same rate.
Gaps in railway tracks prevent buckling due to thermal expansion.
Gases expand less than solids when heated.

Specific Heat Capacity

Specific heat capacity (c) is the energy required to raise the temperature of 1 kg of a substance by 1 °C.
A substance with a low specific heat capacity heats up and cools down quickly.
The equation is: ΔE = m c Δθ, where ΔE is thermal energy (J), m is mass (kg), c is specific heat capacity (J/kg°C), and Δθ is temperature change (°C).

The specific heat capacity of water is 4200 J/kg°C. To raise the temperature of 2 kg of water by 5°C, the energy required is ____ J.

Melting and Boiling

Pure water melts at 0°C and boils at 100°C at atmospheric pressure.
During a change of state (melting or boiling), the temperature remains constant even though energy is being transferred.
The added energy goes into overcoming intermolecular forces (potential energy), not increasing kinetic energy.

What happens to the temperature of a substance while it is melting?

It increases steadily.
It decreases.
It remains constant.
It fluctuates.

Evaporation

Evaporation is a change from liquid to gas that occurs at any temperature, only from the surface of the liquid.
The most energetic molecules escape, reducing the average kinetic energy of the remaining liquid, so the liquid cools.
Factors increasing evaporation rate: higher temperature, larger surface area, and increased air movement.

Which statements about evaporation are true?

Evaporation occurs throughout the liquid.
Evaporation causes cooling of the liquid.
Increasing surface area increases the rate of evaporation.
Evaporation only happens at the boiling point.

Boiling vs Evaporation

Boiling occurs at the boiling point and throughout the liquid; evaporation occurs at any temperature and only at the surface.
Both are changes from liquid to gas.
Boiling requires energy to overcome intermolecular forces throughout the liquid, forming bubbles.

Evaporation occurs at ____ temperature, while boiling occurs only at the ____ point.

Internal Energy

Internal energy is the total energy stored by particles due to their motion (kinetic) and positions (potential).
Heating increases internal energy, raising the average kinetic energy of particles, which increases temperature.
During a change of state, internal energy increases but temperature remains constant as energy goes into potential energy.

What is internal energy?

The energy due to the motion of particles only.
The total energy of particles due to their motion and positions.
The energy required to melt a substance.
The energy transferred by heating.

Investigating Specific Heat Capacity

Aim: determine specific heat capacity by measuring energy supplied (E = IVt) and temperature change.
Equipment: immersion heater, thermometer, ammeter, voltmeter, power supply, digital balance, stopwatch.
Method: heat a known mass of substance, record current, voltage, and temperature at regular intervals.

In the specific heat capacity experiment, how is the thermal energy supplied calculated?

E = m c Δθ
E = I V t
E = m g h
E = 1/2 m v²

Fixed Points of Water

The melting point of pure water is 0°C and the boiling point is 100°C at standard atmospheric pressure.
These are called fixed points and are used to calibrate thermometers.

The upper fixed point on a Celsius thermometer is the ____ point of pure water, which is ____ °C.

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