Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
15 Cards in this Set
- Front
- Back
|
What is specific heat capacity? |
The specific heat capacity of a substance is the amount of energy needed to change the temperature of 1 kg of the substance by 1°C. |
|
|
What is equation used to determine the specific heat capacity? |
E = m × c × θ E is the energy transferred in joules, J m is the mass of the substances in kg c is the specific heat capacity in J / kg °C θ (‘theta’) is the temperature change in degrees Celsius, °C |
|
|
How much energy is needed to increase the temperature of 500 g of lead from 20ºC to 45ºC? The specific heat capacity of lead is 128 J/kg ºC. |
mass of lead = 500 ÷ 1000 = 0.5 kg temperature change = 45 – 20 = 25ºC energy needed = 0.5 × 128 × 25 = 1600 J (1.6 kJ) |
|
|
The specific heat capacity of water is 4181 J/kg/°C and that of lead is 128 J/kg/°C. Which of the following statements is correct? 1 - Lead melts at a low temperature. 2 - More energy is needed to boil water than is needed to boil lead. 3 - More energy is needed to heat water than is needed to heat the same mass of lead by the same amount. |
More energy is needed to heat water than is needed to heat the same mass of lead by the same amount. |
|
|
What is a heat sink? |
A heat sinks is used in computers to cool hot components. It is a block of metal with a large mass attached to the component . Energy from the component is transferred to the heat sink which then transfers the energy to the surrounding air. |
|
A student heats a 1 kg block of aluminium and a 1 kg block of copper to 50 ºC. Explain which block will be storing more energy. |
Aluminium: it has a higher specific heat capacity than copper, so it stores more energy at a given temperature. |
|
|
Why does it take longer to boil a kettle full of water than one only half full? |
There is a greater mass of water in the full kettle, so it takes more energy to raise its temperature by the same amount. If the rate at which energy is transferred to the kettle is the same, it will take longer to heat the larger mass. |
|
Explain why stand-alone radiators are filled with oil, instead of being filled with air. |
Oil has a higher specific heat capacity than air, so it can store more energy. |
|
How much energy does it take to heat up 500 g of lead by 30 ºC? |
Energy transferred = 0.5 kg × 130 J/kg/ºC× 30 ºC = 1950 J |
|
|
A washing machine heats 10 kg of water for each wash cycle. How much energy is saved by washing clothes at 30 ºC instead of 50 ºC? |
Energy saved = 10 kg × 4200 J/kg/ºC× 20 ºC= 840 000 J or 840 kJ |
|
A storage heater contains 100 kg of concrete. 1800 kJ of energy is transferred to it. What is the temperature change of the concrete? |
Temperature change = 1 800 000 J/(100 kg × 900 J/kg/ºC) = 20 ºC |
|
A student heats up a 500 g block of iron from 18 ºC to 46 ºC, using 6280 J of energy. (a) Calculate the specific heat capacity of iron using these results. (b) Suggest why your answer is different to the in the Table. |
448.6 J/kg/ºC Any from the following: the thermometer may not have been calibrated correctly/read correctly; the measurement of energy input may not have been accurate; energy may have been escaping from the block to the surroundings while the measurements were being taken. |
|
Explain why the heat sink in the image shown has fins, and why the metal used to make it should have a high specific heat capacity and be a very good thermal conductor. |
The fins increase the surface area of the metal and so increase the rate at which energy is transferred to the air. A high specific heat capacity means that the metal can absorb a lot of energy without its temperature reaching the temperature of the component it is cooling. The metal must be a good conductor so it can transfer the energy away from the component towards the fins. The faster the energy can be transferred to the fins, the better the temperature difference between the component and the heat sink can be maintained and so the faster the cooling rate. |
|
|
Why do central heating systems use water to transfer heat energy from a boiler to the radiators around a house? |
Water has a very high specific heat capacity - so it can store a lot of energy. |
|
|
What are the key points to remember? |
The energy transferred when the temperature of a material changes depends on its mass, the temperature change and the material from which it is made. The specific heat capacity of a material is the energy needed to raise the temperature of 1 kg of the material by 1 ºC. E = m × c × θ: heat transferred (J) = mass (kg) x specific heat capacity (J/kg/ ºC) x temperature change (ºC) Materials with a high specific heat capacity are used for heat sinks, storage heaters and central heating systems. |
