What internal energy actually is, how heating changes it, and calculating energy using specific heat capacity.
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1.What is internal energy?
The total kinetic energy and potential energy of all the particles in a system.
2.What does heating a system do to its internal energy?
It increases it.
3.What two things can increasing internal energy cause?
A rise in temperature, or a change of state.
4.What does the kinetic energy of the particles determine?
The temperature of the substance.
5.What does the potential energy of the particles depend on?
The separation of the particles, so it changes during a change of state.
6.State the equation for the energy needed to change temperature.
change in thermal energy = mass x specific heat capacity x temperature change
7.Define specific heat capacity.
The energy required to raise the temperature of one kilogram of a substance by one degree Celsius.
8.What are the units of specific heat capacity?
Joules per kilogram per degree Celsius.
9.Calculate the energy to heat 0.5 kg of water by 20 C. Specific heat capacity 4200.
0.5 x 4200 x 20 = 42000 J.
10.A substance needs 9000 J to heat 2 kg by 5 C. Calculate its specific heat capacity.
9000 divided by (2 x 5) = 900 J/kg C.
11.What does a high specific heat capacity mean in practice?
The substance takes a lot of energy to warm up and releases a lot as it cools, so its temperature changes slowly.
12.Why are storage heaters filled with material of high specific heat capacity?
They can store a large amount of energy and release it slowly over a long period.
13.Why does the sea warm up more slowly than the land?
Water has a much higher specific heat capacity than rock and soil.
14.In the specific heat capacity practical, why is the block insulated?
To reduce energy transferred to the surroundings, which would otherwise make the calculated value too high.
15.Why does energy lost to the surroundings make the value too high?
More energy has to be supplied for the same temperature rise, so the calculation suggests the substance needs more energy per degree than it really does.
16.How is the energy supplied measured in that practical?
Using a joulemeter, or by measuring the potential difference, current and time and calculating it.
17.Why is the temperature recorded at regular intervals?
So a graph can be plotted and the temperature rise measured reliably rather than from single readings.
18.What is the difference between heat and temperature?
Temperature measures the average kinetic energy of the particles. Heat refers to energy being transferred because of a temperature difference.
19.Can two objects at the same temperature have different internal energies?
Yes. A larger mass has more particles, so more total energy even at the same temperature.
20.What happens to the particles as a substance is heated without changing state?
They gain kinetic energy and move or vibrate faster, so the temperature rises.
21.Why does a hot drink cool down?
Energy is transferred from the drink to the cooler surroundings until they reach the same temperature.
22.Which has a greater internal energy: 1 kg of water at 20 C or 2 kg at 20 C?
The 2 kg, because there are twice as many particles even though the temperature is the same.
23.State the unit of temperature used in these calculations.
Degrees Celsius, since only the change in temperature is needed.
24.Why does the specific heat capacity equation use a temperature change rather than a temperature?
The energy depends on how much the temperature rises or falls, not on the starting value.
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