Required Practical
Evaluating the method
4.6.2 1
This experiment is used to find the specific heat capacity of brass by assuming that all the thermal energy transferred from the hot water increases the temperature of the lump of brass. We are equating the decrease in thermal energy store of the water to the increase in thermal energy store of the brass. If this assumption is not true, the method will not be valid. 5
The lump of brass has to be moved from one beaker to the other. Consider how this step in the method could affect the accuracy of the results.
6
The energy transferred from the water to the brass will cause the lump of brass in the second beaker to get hotter. Why will the energy transferred to the lump of brass not be stored there permanently?
7
What are the implications of your answers to questions 5 and 6 for the way the experiment is carried out?
8
Why is it important that the lump of brass is covered in water in the second beaker?
KEY INFORMATION When thinking about this experiment, remember that energy tends to move from hotter areas to cooler ones.
Using the data to calculate a value for SHC We find the specific heat capacity of brass by calculating the energy transferred into the brass when its temperature increases and equating that to energy transferred out of the water when its temperature decreases. Decrease in thermal energy of water = increase in thermal energy of brass mwater × cwater × temperature decreasewater = m brass × c brass × temperature increasebrass The final temperature of the water and brass is the same (they reach thermal equilibrium). As long as we know the values of the mass of water, mass of brass, specific heat capacity of water and initial temperatures of the water and brass, we can find the unknown value for the specific heat capacity of brass. 9
There is 250g of water (cwater = 4200 J/kg ° C) in the second beaker and its temperature rises from 17 ° C to 26 ° C. Determine how much energy has been transferred into it.
10 How much energy can we assume has been transferred out of
the brass when it is put into the second beaker? 11 If the brass had been in boiling water, by how much would its
temperature have decreased? 12 The lump of brass has a mass of 150 g. Calculate the specific heat
capacity of brass. 13 Explain why is this method likely to give a lower value for the
specific heat capacity than its true value.
Google search: ‘specific heat capacity by method of mixtures’
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