Change of state

Question 1

Why does heating a system change its internal energy?

Answer 1

• Heating increases the kinetic energy of particles.
• This either raises the temperature or causes a change of state.
• The internal energy is the total of the kinetic and potential energy of particles.

Question 2

What happens when a solid melts or a liquid evaporates?

Answer 2

• When a solid melts, heat energy breaks the bonds between particles.
• When a liquid evaporates or boils, particles gain enough energy to escape as gas.
• No temperature change occurs during a change of state.
• Energy is used to overcome intermolecular forces, not to increase kinetic energy.

Question 3

Describe the arrangement and movement of particles in solids, liquids, and gases.

Answer 3

• Solids: Particles are tightly packed, vibrate in fixed positions, strong forces.
• Liquids: Particles are close but can move, weaker forces, take shape of container.
• Gases: Particles are far apart, move randomly and quickly, negligible forces.

Question 4

How can a temperature-time graph be used to show changes of state?

Answer 4

Method:
1. Heat a solid (e.g., ice) at a constant rate and record temperature over time.
2. Plot a temperature-time graph.
3. The graph has flat sections (plateaus) where temperature does not increase.
4. These sections represent melting or boiling.
5. Energy is used to break bonds, not to raise temperature.
6. The graph shows the latent heat required for state changes.

Question 5

What is specific heat capacity?

Answer 5

• The energy needed to raise the temperature of 1 kg of a substance by 1°C.
• Measured in J/kg°C.
• Different materials have different SHC values.

Question 6

What is the equation for specific heat capacity?

Answer 6

• The equation is: ΔQ = m c ΔT
  
  • ΔQ = thermal energy change (J)
  • m = mass (kg)
  • c = specific heat capacity (J/kg°C)
  • ΔT = temperature change (°C)

Question 7

How can the specific heat capacity of a material be measured?

Answer 7

Equipment:
- Block of material, immersion heater, thermometer, ammeter, voltmeter, stopwatch.

Method:
1. Measure the mass of the block.
2. Insert a heater and thermometer into the block.
3. Turn on the heater and measure energy supplied (using voltage and current).
4. Record temperature change over time.
5. Use ΔQ = m c ΔT to calculate c.
6. Improvements: Reduce heat loss using insulation.