(c) change of state

what will heating a system do and why (5.8P)

change the energy stored within a system because …

raise its temperature because…

produce changes of state because …

changes that occur when a solid melts to form a liquid (5.9P)

when a solid is heated, its particles gain more energy, making them vibrate more. this weakens the forces that hold a solid together in its rigid structure, making the solid expand. at a certain temperature (the melting point, which varies from substance to substance e.g. the melting point of ice is 0 degrees celsius), the particles have enough energy to break free from their positions and instead slide over each other, shifting the solid into a liquid.

changes that occur when a liquid evaporates / boils to form a gas (5.9P)

when a liquid is heated, its particles will gain more energy, making the particles move faster. this weakens and breaks the bonds holding the liquid together. at the boiling point (which also varies from substance to substance e.g. the boiling point of water is 100 degrees celsius), the particles have enough energy to break their bonds and move further apart, shifting the liquid into a gas.

describe the arrangement and motion of particles in a solid (5.10P)

bonds between particles: strongest energy of a given particle is a combination of potential and kinetic

particle arrangement: regular arrangement. many (pure) solids have particles arranged in a lattice, the solid as a whole has a fixed shape. solids are not very compressible

particle motion: particles vibrate about a fixed position. particles don’t “change neighbours”. the amplitude and frequency of the vibration depends on the temperature of the solid

describe the arrangement and motion of particles in a liquid (5.10P)

bonds between particles: less strong than in solids. less potential energy and more kinetic

particle arrangement: particles are still closely packed (densities of solids and liquids are similar). random arrangement that is not fixed (changes over time)

particle motion: particles “slide over” each other; particles change neighbours. liquids flow and can take the shape of their container

describe the arrangement and motion of particles in a gas (5.10P)

bonds between particles: very weak. almost non-existent. the “ideal gas” (“classical gas”) has no bonds between particles, they are all in the particles. energy is in the form of kinetic energy

particle arrangement: no arrangement. very large distances between particles in comparison to the sizes of the particles themselves

particle motion: particles move in straight lines in random directions at a variety of speeds (the mean speed depends on the gas’s temperature) until the particle collides with the walls of its container

obtain a temperature-time graph to show the constant temperature during a change of state (5.11P)

• remove the boiling tube of stearic acid from
  the water bath

• place the tube into a beaker of room
  temperature water

• add a separate thermometer to the water

• take readings from the thermometer in the
  stearic acid and the water every minute
  [make sure to avoid parallax error while doing so]

• note readings in the table below

• note on the table when you observe the stearic
  acid change from a liquid to a solid.

• plot your results in a graph

specific heat capacity (5.12P)

energy required to change the temperature of an object by one degree celsius per kilogram of mass (J/ kg °C)

equation for change in thermal energy (5.13P)

change in thermal energy = mass × specific heat capacity × change in temperature

ΔQ = m × c × ΔT

investigate the specific heat capacity of materials including water and some solids (5.14P)

• set up the apparatus as shown the diagram.

• make note of all measurements: current (A), potential difference (V), mass (kg).

• use the electronic balance to measure the mass of your

• record the initial temperature of you block.

• switch on the heater and start your stopwatch.
  [you will now leave the heater on for 10 minutes]

• while the heater is switched on take readings from the
  ammeter and the voltmeter.

• use these to calculate the thermal energy that will be
  supplied to the block in 10 minutes

• record the temperature of your block after 10 minutes.

• calculate the change in temperature