[Music] hi and welcome back to free science lessons. co.uk by the end of this video you should be able to calculate the amount of energy stored in or released from a system as its temperature changes I'm showing you here some water boiling and the question is how much energy is stored in hot water in order to answer that we need to look at the idea of specific heat capacity the specific capacity of a substance is the amount of energy required to raise a temperature of 1 kg of the substance by 1° C now that sounds tricky but it's actually straightforward so let's take a look at a sample question calculate the energy required to increase a temperature of 2 kg of water from 20° C to 100° C the specific heat capacity of water is 4,200 Jew per kilogram per de C to answer this question we've got to use this equation and you are given this in the exam the change in thermal energy in Jewels equals the mass in kilogram multiplied by the specific heat capacity multiplied by the temperature change in degrees C we've got 2 kilog of water the specific capacity of water is 4,200 Jew per kilogram per degre C and you will be given that value in the exam and finally the temperature change in this case is 80° C putting these values into the equation gives us a total change in thermal energy of 67200 Jew we can convert that to KJ by dividing by 1,000 giving us 672 K here's a question for you an ion has an aluminium plate with a mass of 1.5 kg calculate the thermal energy stored in the plate when the temperature rises from 20° C to 200° C the specific capacity of aluminium is 913 Jew per kilog per de C pause a video and try this question yourself okay so we've got a mass of 1.5 kg this specific capacity Valu minum is 913 JW per kilogram per de C and the change in temperature is 180° C putting these into the calculation gives us a total change in thermal energy of 246,000 510 Jew we can also convert that to kles giving us a value of 24651 K here's a final question for you to try a hot water bottle cools down from 80° C to 20° C releasing 76,000 Jew of thermal energy calculate the mass of water in the hot water bottle the specific capacity of water is 4,200 Jew per kilogram per Dee C now to answer this question you're going to have to rearrange the equation to find the mass pause the video and try this yourself okay I've rearranged the equation to calculate mass and here it is the thermal energy change is 756 th000 Jew the specific capacity of water is 4,200 Jew per kilg per de C and the temperature change is 60° C putting these into the equation gives us a mass of 3 kg and that's our final answer remember you'll find plenty more questions on specific capacity in my vision workbook and you can get that by clicking on the link above okay so hopefully now you should be able to calculate the amount of energy stored in or released from a system as its temperature changes [Music]