# OCR - P6: Matter – models and explanations

 P6.1 How does energy transform matter? Background to the topic What you should be able to do: It took the insight of a number of eighteenth and nineteenth century scientists to appreciate that heat and work were two aspects of the same quantity, which we call energy. Careful experiments devised by Joule showed that equal amounts of mechanical work would always produce the same temperature rise. Energy can be supplied to raise the temperature of a substance by heating using a fuel, or an electric heater, or by doing work on the material. Mass – the amount of matter in an object – depends on its volume and the density of the material of which it consists. Different substances store different amounts of energy per kilogram for each °C temperature rise – this is called the specific heat capacity of the material. When a substance in the solid state is heated its temperature rises until it reaches the melting point of the substance, but energy must continue to be supplied for the solid to melt. Its temperature does not change while it melts, and the change in density on melting is very small. Similarly as a substance in the liquid state is heated its temperature rises until it reaches boiling point; its temperature does not change, although energy continues to be supplied while it boils. The change in density on boiling is very great; a small volume of liquid produces a large volume of vapour. Different substances require different amounts of energy per kilogram to change the state of the substance – this is called the specific latent heat of the substance. 1. a) define density b) describe how to determine the densities of solid and liquid objects using measurements of length, mass and volume In your practical work you will devise a method to measure the density of irregular objects. You will also measure the specific heat capacity of a range of substances such as water, copper, aluminium. You will also measure the latent heat of fusion of a substance in the solid state and the latent heat of vaporisation of a substance in the liquid state. To show that the same amount of work always results in the same temperature rise. You will collect data, plot and interpret graphs that show how the temperature of a substance changes when heated by a constant supply of energy. 2. Recall and apply the relationship between density, mass and volume to changes where mass is conserved: density (kg/m3) = mass (kg) ÷ volume (m3) 3. Describe the energy transfers involved when a system is changed by heating (in terms of temperature change and specific heat capacity) 4. Define the term specific heat capacity and distinguish between it and the term specific latent heat 5. a) select and apply the relationship between change in internal energy of a material and its mass, specific heat capacity and temperature: change in internal energy (J) = mass (kg) × specific heat capacity (J/kg°C) × change in temperature (°C) b) explain how to safely use apparatus to determine the specific heat capacity of materials 6. Select and apply the relationship between energy needed to cause a change in state, specific latent heat and mass: energy to cause a change of state (J) = mass (kg) × specific latent heat (J/kg) You should be able to describe and explain how careful experimental strategy can yield high quality data and how developing a new scientific explanation takes creative thinking 7. Describe all the changes involved in the way energy is stored when a system changes, and the temperature rises, for example: a moving object hitting an obstacle, an object slowing down, water brought to a boil in an electric kettle 8. Make calculations of the energy transfers associated with changes in a system when the temperature changes, recalling or selecting the relevant equations for mechanical, electrical, and thermal processes