Edexcel IGCSE Physics - Changes of State

what are the three states of matter?

• solid

• liquid

• gas

describe the arrangement and motion of particles in a solid

• strong forces of attraction hold the particles close together in a fixed, regular arrangement

• particles don’t have much energy so they can only vibrate about their fixed positions

describe the arrangement and motion of particles in a liquid

• weaker forces of attraction between the particles

• particles are close together that can move past each other and form irregular arrangements

• they have more energy than particles in a solid

• they move in random directions at low speeds

describe the arrangement and motion of particles in a gas

• virtually no forces of attraction between the particles

• particles have the most energy out of the 3 states

• they are free to move

• travel in random directions at high speeds

what will a heating system do?

• it will increase the kinetic energy store of the particles that are being heated

• this will raise its temperature (average kinetic energy of particles) or cause a change of state

describe the changes in state for all changes

describe the changes that occur when a solid melts to become a liquid

• when you heat a solid extra energy is transferred to the particles’ kinetic energy stores - making them vibrate faster

• at some point, the energy will be enough to partly overcome the forces of attraction between the particles and the particles begin to move around

describe the changes that occur when a liquid boils to become a gas

• when you heat a liquid, energy is transferred to the particle’s kinetic energy stores making them moving faster

• eventually when enough of the particles have enough energy to overcome their attraction to each other, the liquid begins to boil

describe the general changes that occur during condensation or freezing

energy is given out to the surroundings which causes bonds to form between particles

what is evaporation?

• when singular particles escape from a liquid to become gas particles - can happen at temperatures lower than a liquid boiling point

• particles near the surface can evaporate if they are:

  • travelling in the right direction to escape the liquid

  • they are travelling fast enough to overcome the attractive forces of other particles in the liquid

what does evaporation result in?

• the fastest particles are most likely to evaporate from the liquid

• the average speed and energy in the kinetic energy stores of the remaining particles decreases

• this mean that the temperature of the remaining liquid decreases

what happens to the temperature when a change of state occurs?

it remains constant as all energy is transferred to the weakening of forces of attraction or released as they are strengthened

what graph can be used to show changes of state?

temperature(y)-time(x) graph

what doe straight lines on a temperature-time graph show?

changes of state - first is melting point, second boiling point

what do diagonal lines on a temperature-time graph show?

increases (or decreases) in temperature

how would you obtain a temperature time graph for water?

• fill a beaker with crushed ice

• place a thermometer into the beaker and record the temperature of the ice

• gradually heat the beaker full of ice with a bunsen burner

• every 20 secs record the temperature and state of the water until it begins to boil

• plot a graph

what is the specific heat capacity?

the energy required to change the temperature of an object by 1C per kilogram of mass

what is the equation for specific heat capacity?

change in thermal energy (Q/J) = mass (m/kg) x specific heat capacity (c/ J/kgC) x change in temperature (T/C)

describe an experiment to find the specific heat capacity of water

• use a mass balance to measure the mass of an insulating container

• fill the container with water and measure the mass again, calculate the mass of water

• set up the experiment as shown - put a lid on container, make sure joulemeter (can also use ammeter and voltmeter as well as stopwatch - E=IVt) is at 0

• measure the temperature of the water then turn on the power

• when the temperature has increased by 10C switch off the power and record the increase as well as the joulemeter reading

• repeat the experiment and calculate means

• calculate specific heat capacity using the equation

how would you modify this for a solid?

• use a block of material of known mass with insulating material wrapped around it

• make sure the block has two holes

• don’t record the final temperature until it has stopped increasing

what is the main problem with this experiment?

heat loss to the surroundings