## Overview This topic introduces the idea that the internal energy of a system is the sum of the potential and kinetic energy of its molecules. It considers the internal energy of an ideal gas and discusses energy transfer between a gas and its surroundings. The first law of thermodynamics is introduced in the form ΔU = Q – W. ## Working Scientifically The specified practical work within this unit contains opportunities for learners to plot and interpret graphs; to process and analyse data using appropriate mathematical skills; to apply investigative approaches to practical work; to follow written instructions; to make and record observations; to keep appropriate records of experimental activities; to use appropriate analogue apparatus and digital instruments to record a range of measurements. ## Mathematical Skills There are a number of opportunities for the development of mathematical skills in this unit. These include using ratios, fractions and percentages; estimating results; making order of magnitude calculations; understanding and using the symbols =, <, <<, >>, >, ∝, ≈; translating information between graphical, numerical and algebraic forms; plotting two variables from experimental/other data. ## How Science Works There are opportunities within this topic for learners to use their knowledge and understanding to pose scientific questions, define scientific problems, present scientific arguments and scientific ideas; to analyse and interpret data to provide evidence, recognise correlations and causal relationships; to communicate information and ideas in appropriate ways using appropriate terminology. Learners can be given the opportunity to carry out experimental work to investigate the specific heat capacity of different materials and use their findings together with data about the thermal conductivity of materials to investigate methods of insulating buildings to produce optimum heat retention. ### Learners should be able to demonstrate and apply their knowledge and understanding of: (a) the idea that the internal energy of a system is the sum of the potential and kinetic energies of its molecules (b) absolute zero being the temperature of a system when it has minimum internal energy (c) the internal energy of an ideal monatomic gas being wholly kinetic so it is given by 3 U nRT 2 = (d) the idea that heat enters or leaves a system through its boundary or container wall, according to whether the system's temperature is lower or higher than that of its surroundings, so heat is energy in transit and not contained within the system (e) the idea that if no heat flows between systems in contact, then they are said to be in thermal equilibrium, and are at the same temperature (f) the idea that energy can enter or leave a system by means of work, so work is also energy in transit (g) the equation W p V =  can be used to calculate the work done by a gas under constant pressure (h) the idea that even if p changes, W is given by the area under the p – V graph (i) the use of the first law of thermodynamics, in the form  = − U Q W and know how to interpret negative values of ΔU, Q, and W (j) the idea that for a solid (or liquid), W is usually negligible, so Q = ΔU (k) Q mc =  , for a solid or liquid, and this is the defining equation for specific heat capacity, c [[Specified Practical Work]] - Estimation of absolute zero by use of the gas laws - Measurement of the specific heat capacity for a solid