Thermal Properties And Temperature

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Notes de leçon

Thermal Expansion

When a material is heated at constant pressure, its temperature increases, volume increases (expands), and density decreases.
Expansion occurs because molecules gain kinetic energy, move/vibrate faster, and push each other apart.
For equal temperature rise, gases expand most, solids least, and liquids in between.
Liquid-in-glass thermometers use thermal expansion: liquid in bulb expands into narrow capillary tube; scale measures temperature.
Temperature-activated switches use a bimetallic strip (two metals with different expansion rates) that bends when heated to close a circuit.
Unwanted expansion can cause buckling in railway tracks, roads, and bridges; expansion gaps are built in to allow safe expansion.

Thermal expansion diagram

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 thermal energy is added or removed.
Added energy goes into the potential store (overcoming intermolecular forces), not the kinetic store, so temperature stays constant.
Melting: solid → liquid; particles gain ability to flow but remain close together.
Boiling: liquid → gas; intermolecular forces are completely overcome; bubbles form throughout the liquid.
Condensation (gas → liquid) and solidification (liquid → solid) release energy; temperature stays constant during the change.

Heating curve showing changes of state

Evaporation

Evaporation is a change of state 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 of the remaining liquid → cooling effect.
Rate of evaporation increases with higher temperature, larger surface area, and greater air movement (wind/fan).
Boiling vs evaporation: boiling occurs at the boiling point throughout the liquid; evaporation occurs at any temperature only at the surface.

Evaporation of liquid molecules

Liquid-in-Glass Thermometer (Extended Tier)

Sensitivity increases if the capillary tube diameter is reduced (same volume change gives longer liquid column) or if the bulb volume is increased (more liquid expands further).
Range is affected by the length of the capillary tube and the amount of liquid; a smaller bulb (less mercury) reduces the range because less expansion occurs.

Liquid-in-glass thermometer

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1.State the fixed point on the Celsius scale for the melting point of pure water.
Easy
- A0
- B2
- C-1
- D1
2.State the fixed point on the Celsius scale for the boiling point of pure water.
Easy
- A120
- B90
- C110
- D100
3.Equal volumes of steel, oil and hydrogen are heated from 20 °C to 60 °C. Which substance has the greatest increase in volume?
Medium
- Asteel
- Boil
- Chydrogen
- Dall increase by the same amount
4.State the temperature reading on a liquid-in-glass thermometer that shows the liquid level exactly at the 20 °C mark.
Easy
5.State the temperature range of a liquid-in-glass thermometer that measures from -10 °C to 110 °C.
Easy
6.Describe, in terms of molecules, what happens when a liquid evaporates.
Medium
7.State two changes in the weather that help wet clothes to dry more quickly.
Easy
8.Explain, in terms of molecules, how thermal expansion takes place in a liquid.
Medium

Plus de questions

9.Complete the sentence about relative expansion.
Medium
For equal volumes at equal pressures for equal temperature rises, solids expand ____ compared to liquids, and gases expand ____ compared to liquids.
10.State one use of thermal expansion.
Easy
11.State one way engineers minimise the issue of thermal expansion in metal railway tracks.
Easy
12.State and explain any effect on the sensitivity of a liquid-in-glass thermometer of reducing the diameter of the capillary tube.
Hard
13.What happens to the volume of a gas when it is heated at constant pressure?
Easy
- AIt decreases
- BIt increases
- CIt stays the same
- DIt first increases then decreases
14.Which state of matter expands the most when heated at constant pressure?
Easy
- ASolid
- BLiquid
- CGas
- DAll expand equally
15.During melting, the temperature of a substance increases.
Easy
True or false?
16.Evaporation can occur at any temperature between the melting point and boiling point of a liquid.
Medium
True or false?
17.A bimetallic strip is made of two different metals. When heated, it bends. Why does this happen?
Medium
- ABoth metals expand by the same amount
- BOne metal expands more than the other
- CThe metals contract
- DThe strip becomes magnetic
18.Match each process with its correct description.
Easy
- Melting
- Boiling
- Condensation
- Solid to liquid
- Liquid to gas throughout
- Gas to liquid
19.Arrange the following steps in the correct order to describe what happens when a solid is heated until it becomes a gas.
Medium
- Solid expands
- Solid melts to liquid
- Liquid boils to gas
- Temperature remains constant during melting and boiling
20.Which of the following are true about evaporation? (Select all that apply)
Medium
- AOccurs at any temperature
- BOccurs throughout the liquid
- CCools the liquid
- DOnly occurs at the boiling point
- EInvolves only the most energetic molecules at the surface
21.During boiling, the temperature of the liquid increases as more heat is added.
Easy
True or false?
22.Which of the following factors increases the rate of evaporation of a liquid?
Medium
- ADecreasing the temperature
- BDecreasing the surface area
- CIncreasing air movement over the surface
- DIncreasing the humidity of the air
23.Which statements about condensation are correct? (Select all that apply)
Medium
- AIt is a change from gas to liquid
- BIt occurs at any temperature
- CTemperature remains constant during condensation
- DEnergy is transferred away from the system
- EIt is the same as evaporation
24.A student is investigating the expansion of a gas. A sealed syringe containing air is heated from 20 °C to 80 °C at constant pressure. Which statement correctly describes the effect on the air molecules?
Medium
- AThe molecules vibrate more and move closer together, decreasing the volume.
- BThe molecules move faster and push each other further apart, increasing the volume.
- CThe molecules expand because they get bigger when heated.
- DThe molecules slow down and the volume decreases.
25.The graph shows the temperature of a pure substance as it is heated at a constant rate. Which section of the graph corresponds to the substance being heated as a liquid?
Hard
- AA
- BB
- CC
- DD
26.Which of the following statements about evaporation are correct? (Select all that apply)
Medium
- AEvaporation occurs only at the boiling point of the liquid.
- BEvaporation occurs only from the surface of the liquid.
- CEvaporation causes cooling of the remaining liquid.
- DEvaporation happens throughout the whole liquid.
27.During boiling, the temperature of a pure liquid remains constant even though heat is being added.
Easy
True or false?
28.A bimetallic strip consists of brass (which expands more) and invar (which expands less) joined together. When the strip is heated, which way does it bend?
Medium
- AIt bends towards the brass side.
- BIt bends towards the invar side.
- CIt does not bend because both metals expand.
- DIt bends in a random direction.
29.A student is investigating the thermal expansion of a metal rod. She measures the length of the rod at 20 °C and again after heating it to 100 °C. Which of the following is the most likely reason for the increase in length?
Medium
- AThe metal atoms themselves expand when heated.
- BThe metal atoms vibrate more and move further apart.
- CThe metal atoms increase in number as the temperature rises.
- DThe metal atoms become larger due to the absorption of heat.
30.A liquid-in-glass thermometer is used to measure the temperature of a hot liquid. Which of the following changes to the thermometer would make it more sensitive (i.e., show a larger change in liquid length for the same temperature change)?
Medium
- AUsing a smaller bulb containing less liquid.
- BUsing a narrower capillary tube.
- CUsing a liquid that expands less when heated.
- DUsing a thicker glass wall for the bulb.
31.A student places a sealed syringe containing a fixed mass of air into a water bath at 20 °C. The piston is free to move. She then heats the water bath to 80 °C. Which statement correctly describes what happens to the volume of the air and the pressure inside the syringe?
Medium
- AVolume increases, pressure remains constant.
- BVolume increases, pressure increases.
- CVolume remains constant, pressure increases.
- DVolume decreases, pressure remains constant.
32.Which of the following is the fixed point on the Celsius scale for the melting point of pure water?
Easy
- A0 °C
- B100 °C
- C32 °C
- D212 °C
33.When a solid is heated at constant pressure, its volume increases. What is the main reason for this thermal expansion?
Medium
- AThe molecules themselves expand.
- BThe molecules vibrate more and push each other apart.
- CThe molecules increase in mass.
- DThe number of molecules increases.
34.During melting, the temperature of a substance remains constant.
Easy
True or false?
35.Match each fixed point of water with its correct temperature.
Easy
- Melting point of pure water
- Boiling point of pure water
- 0 °C
- 100 °C
36.Arrange the following steps in the correct order to describe how a bimetallic strip works when heated.
Easy
- The strip bends
- The two metals expand by different amounts
- The strip is heated
- One metal expands more than the other
37.A student heats a metal rod at constant pressure. Which statement correctly describes what happens to the molecules in the rod?
Medium
- AThe molecules expand.
- BThe molecules vibrate more and push each other apart.
- CThe molecules increase in mass.
- DThe molecules move closer together.
38.A bimetallic strip is made of brass (expands more) and invar (expands less). When the strip is cooled, which way does it bend?
Medium
- ATowards the brass side
- BTowards the invar side
- CIt does not bend
- DIt bends in a random direction
39.Which of the following are true about the fixed points of pure water at atmospheric pressure? (Select all that apply)
Medium
- AThe melting point is 0 °C.
- BThe boiling point is 100 °C.
- CThe melting point is 100 °C.
- DThe boiling point is 0 °C.
- EBoth fixed points are independent of pressure.
40.During melting, the temperature of a pure substance remains constant even though thermal energy is being added.
Easy
True or false?
41.A student places a sealed syringe containing a fixed mass of air into a water bath at 20 °C. The piston is free to move. She then heats the water bath to 80 °C. Which statement correctly describes what happens to the volume and the density of the air in the syringe?
Medium
- AVolume increases, density decreases.
- BVolume decreases, density increases.
- CVolume increases, density increases.
- DVolume decreases, density decreases.
42.Which of the following factors does NOT increase the rate of evaporation of a liquid?
Easy
- AIncreasing the temperature of the liquid
- BIncreasing the surface area of the liquid
- CDecreasing the air movement above the liquid
- DIncreasing the air movement above the liquid
43.A student uses a liquid-in-glass thermometer to measure the temperature of a hot water bath. The thermometer has a bulb containing a large volume of liquid and a narrow capillary tube. Which change would increase the sensitivity of the thermometer?
Medium
- AUsing a liquid that expands less for the same temperature change
- BMaking the capillary tube wider
- CMaking the bulb smaller
- DUsing a liquid that expands more for the same temperature change
44.Which of the following are correct about the melting of a pure solid? (Select all that apply)
Medium
- AThe temperature remains constant during melting
- BThe internal energy of the substance increases during melting
- CThe molecules lose kinetic energy during melting
- DEnergy is used to overcome intermolecular forces
45.Evaporation occurs only at the boiling point of a liquid.
Easy
True or false?
46.When a solid is heated at constant pressure, its molecules expand.
Easy
True or false?
47.The melting point of pure water at atmospheric pressure is 0 °C.
Easy
True or false?
48.A liquid-in-glass thermometer contains a bulb of liquid and a narrow capillary tube. Which change would make the thermometer more sensitive?
Medium
- AUsing a liquid that expands less
- BMaking the bulb larger
- CMaking the capillary tube wider
- DUsing a smaller bulb
49.Complete the sentence.
Easy
The fixed point on the Celsius scale for the melting point of pure water is ____ °C.
50.State one factor that increases the rate of evaporation of a liquid.
Easy
51.A liquid-in-glass thermometer has a bulb containing 0.5 cm³ of alcohol. The alcohol expands by 0.02 cm³ when heated from 20 °C to 50 °C. What is the volume of alcohol at 50 °C?
Easy
52.Explain, in terms of molecules, why the temperature remains constant during boiling.
Medium
53.Describe an experiment to investigate how the rate of evaporation of a liquid depends on the temperature of the liquid.
Hard
54.A liquid-in-glass thermometer has a bulb containing 0.5 cm³ of alcohol. The alcohol expands by 0.02 cm³ when heated from 20 °C to 50 °C. What is the volume of alcohol at 50 °C?
Easy
- A2.52 cm³
- B-0.48 cm³
- C1.52 cm³
- D0.52 cm³

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