Temperature and Energy

What are my objectives while studying this topic?


The main aim of this topic is to establish the links between temperature, heat energy and the materials that things are made out of.


Why is this important?


If you can get to grips with this then you will be able to see why certain materials can be used as conductors and others as insulators, and you will be able to gauge the thermal usefulness of materials. Also, you will understand the concepts of specific heat capacity and specific latent heat, and the main measures of a material’s ability to be heated and boiled!


Can I get an introduction to this topic?


Yes, why not have a look at the following clip:



So, let’s get to it: what is the difference between ‘temperature’ and ‘heat energy’?
This is a tricky concept! If things have a lot of ‘heat energy’, are they always ‘hot’? It turns out that the type of material that the ‘thing’ is made out of makes a big difference, so does the amount of 'stuff' the 'thing' it is made out of. The 'stuff' is the molecules the material or 'thing' is made out of. Different materials (molecules) need different amounts of energy to heat them up. So, in short, more material needs more energy to heat it up!


On a molecular level temperature is directly proportional to the mean kinetic energy of the molecules. A higher temperature means more kinetic energy. If a material is heated by a heat source (such as a fire, or an electric heating element), then the amount of heat energy supplied by the source is shared by all the molecules in the material. This increases their kinetic energy and so increases their temperature, causing the material to heat up.


A simple way of visualising this is to compare a hand-held Bonfire-night sparkler and a bath of tepid water. The sparkler is very hot – it has a high temperature because the energy is shared by (relatively) few molecules. Its total heat energy however is very low. A tepid bath of water has a low temperature, but very high heat energy because there are a lot of molecules!


What is the definition of heat capacity?


Specific heat capacity, also known simply as specific heat, is the measure of the heat energy required to increase the temperature of a unit quantity of a substance by a certain temperature interval. The term originated primarily through the work of Scottish physicist Joseph Black who conducted various heat measurements and used the phrase "capacity for heat". More heat energy is required to increase the temperature of a substance with high specific heat capacity than one with low specific heat capacity. For instance, eight times the heat energy is required to increase the temperature of an ingot of magnesium as is required for a lead ingot of the same mass.


What is the definition of specific latent heat of vapourisation?


The specific latent heat of vaporization of a liquid substance is the heat required to change one kilogram of it from liquid to vapour without any temperature change.

What is the definition of specific latent heat of fusion?


The specific latent heat of fusion of a solid substance is the heat required to change one kilogram of it from solid to liquid without any temperature change.


What will I be expected to be able to do after studying this topic?


Know, use and apply the concepts of specific heat capacity and specific latent heat of vaporisation in the context of the use of carbon-based (fossil) fuels to generate heat and electricity.


What are the key words to learn and use for this topic?


  • Specific heat capacity

  • Specific latent heat

  • Vaporisation

  • Fusion

  • Thermal energy

  • Calorimeter


How long will this topic take to study?


On average you’ll be looking at about five hours of study time.


What are the main activities on this topic?


Experiment!


Measure the specific heat capacity of a metal block and water.


How?


Use a small 12V electric heater to supply heat energy to an insulated metal block and an insulated cup of water.


Any references for this?



You must produce a suitable Risk Assessment for this activity



Experiment!


Measure the specific latent heat of vaporisation of water.

 

How?


This is difficult (safety wise) without specially designed apparatus. If you have access to such apparatus use it to measure lv. A much safer alternative involving measurement of the specific latent heat of fusion lf is outlined below.


Any references for this?


 

You must produce a suitable Risk Assessment for this activity



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