# KS4 Kinetic Theory

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# Yr 9 Kinetic Theory Learning Objectives

Students should understand the following:

• The amount of energy stored in or released from a system as its temperature changes can be calculated using the equation: change in thermal energy = mass× specific heat capacity × temperature change Δ E = m c Δ θ
• The specific heat capacity of a substance is the amount of energy required to raise the temperature of one kilogram of the substance by one degree Celsius.
• The density of a material is defined by the equation: density = mass/volume (ρ = m/V)
• The particle model can be used to explain:
• the different states of matter
• differences in density.
• Students should be able to recognise/draw simple diagrams to model the difference between solids, liquids and gases.
• Students should be able to explain the differences in density between the different states of matter in terms of the arrangement of atoms or molecules.
• Students should be able to describe how, when substances change state (melt, freeze, boil, evaporate, condense or sublimate), mass is conserved.
• Changes of state are physical changes which differ from chemical changes because the material recovers its original properties if the change is reversed.
• Energy is stored inside a system by the particles (atoms and molecules) that make up the system. This is called internal energy.
• Internal energy is the total kinetic energy and potential energy of all the particles (atoms and molecules) that make up a system.
• Heating changes the energy stored within the system by increasing the energy of the particles that make up the system. This either raises the temperature of the system or produces a change of state.
• If the temperature of the system increases, the increase in temperature depends on the mass of the substance heated, the type of material and the energy input to the system.
• If a change of state happen, the energy needed for a substance to change state is called latent heat.
• When a change of state occurs, the energy supplied changes the energy stored (internal energy) but not the temperature.
• The specific latent heat of a substance is the amount of energy required to change the state of one kilogram of the substance with no change in temperature.
• Energy for a change of state = mass × specific latent heat (E = m L)
• Specific latent heat of fusion – change of state from solid to liquid
• Specific latent heat of vaporisation – change of state from liquid to vapour
• Students should be able to interpret heating and cooling graphs that include changes of state.
• Students should be able to distinguish between specific heat capacity and specific latent heat.
• The molecules of a gas are in constant random motion. The temperature of the gas is related to the average kinetic energy of the molecules.
• Changing the temperature of a gas, held at constant volume, changes the pressure exerted by the gas.
• Students should be able to:
• explain how the motion of the molecules in a gas is related to both its temperature and its pressure
• explain qualitatively the relation between the temperature of a gas and its pressure at constant volume.
• A gas can be compressed or expanded by pressure changes. The pressure produces a net force at right angles to the wall of the gas container (or any surface).
• Students should be able to use the particle model to explain how increasing the volume in which a gas is contained, at constant temperature, can lead to a decrease in pressure.
• For a fixed mass of gas held at a constant temperature: pressure × volume = constant (p V = constant)
• Students should be able to calculate the change in the pressure of a gas or the volume of a gas (a fixed mass held at constant temperature) when either the pressure or volume is increased or decreased.
• Work is the transfer of energy by a force.
• Doing work on a gas increases the internal energy of the gas and can cause an increase in the temperature of the gas.
• Students should be able to explain how, in a given situation eg a bicycle pump, doing work on an enclosed gas leads to an increase in the temperature of the gas.

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