Internal energy and energy transfers Flashcards
Explain what is meant by internal energy in a system and how it is related to the motion and arrangement of the particles that make up the system.
energy is stored inside a system by the particles (atoms
and molecules) that make up the system. This is called
internal energy.
What is meant by internal energy in a system, and how is it related to the kinetic and potential energy of the particles?
nternal energy is the total kinetic energy and potential energy of all the particles (atoms and molecules) that
make up a system.
Explain how heating a system changes the energy of the particles and what two effects it can have on the system.
heating changes the energy stored within the system by
increasing the energy of the particles that make up the
system. This either raises the temperature of the system
or produces a change of state.
Explain how the temperature change of a system depends on:
if the temperature of the system increases, the increase in
temperature depends on
* the mass of the substance heated
* the type of material
* the energy input to the system
What is meant by the specific heat capacity of a substance, and how is it related to the amount of energy required to change the temperature of the substance?
The specific heat capacity of a substance is the amount of
energy required to raise the temperature of one kilogram
of the substance by one degree Celsius.
Explain why the temperature does not change when a substance undergoes a change of state, even though energy is supplied to the system.
if a change of state happens, the energy supplied
changes the energy stored (internal energy) but not the
temperature.
describe how to calibrate a measuring instrument. (e.g. a
thermometer).
How to calibrate a thermometer:
Use a known reference temperature: Choose a reference point with a known temperature, such as the freezing point of water (0°C) or the boiling point of water (100°C) at standard atmospheric pressure (1 atm).
Place the thermometer in the reference substance:
For 0°C, immerse the thermometer in a mixture of ice and water. Ensure it is not touching the sides or bottom of the container.
For 100°C, place the thermometer in boiling water.
Read the thermometer: After the thermometer stabilizes in the substance, read the temperature.
Check and adjust:
If the thermometer does not read the correct reference temperature, adjust it (if it has an adjustment screw) or note the difference between the measured and expected temperatures.
Repeat if necessary: You can also check the thermometer at another known temperature, such as room temperature, to ensure its accuracy.
change in thermal energy:
apply the equation:
change in thermal energy = mass × specific heat capacity
× temperature change
ΔE = m c Δθ
* change in thermal energy, ΔE, in joules, J
* mass, m, in kilograms, kg
* specific heat capacity, c, in joules per kilogram per
degree Celsius, J/kg °C
* temperature change, Δθ, in degrees Celsius, °C.
energy for a change of state
apply the equation:
energy for a change of state = mass × specific latent heat
E = m L
* energy, E, in joules, J
* mass, m, in kilograms, kg
* specific latent heat, L, in joules per kilogram, J/kg
describe and experiment to measure the latent heat of
fusion of water
Apparatus:
Ice (at 0°C)
Beaker or calorimeter
Balance (to measure mass)
Thermometer
Power supply (e.g., an electrical heater)
Stopwatch
Insulated container
Electrical heater (or immersion heater)
Joules meter or ammeter and voltmeter (optional, to measure energy input)
Method:
Weigh the ice:
Use a balance to measure the mass of the ice (in kg). This will be the mass
𝑚
m of ice.
Set up the equipment:
Place the ice in a beaker or calorimeter and set up the electrical heater so that it will melt the ice. Ensure the thermometer is in the ice-water mixture to measure the temperature.
Start heating:
Switch on the heater to start melting the ice. Record the time taken for the ice to completely melt.
Measure temperature and energy input:
Monitor the temperature using the thermometer to ensure it remains at 0°C during the melting process.
Use the ammeter and voltmeter to measure the current and voltage supplied to the heater. If you are using an electrical heater, the energy supplied can be calculated using the formula:
Energysupplied(J)
=
Voltage(V)
×
Current(I)
×
Time(t)
Energysupplied(J)=Voltage(V)×Current(I)×Time(t)
Alternatively, if you have a joules meter, it will directly measure the energy supplied to the ice.
Calculate the latent heat of fusion:
The latent heat of fusion
𝐿
𝑓
L
f
is given by the formula:
𝐿
𝑓
=
Energysupplied(J)
Massofice(kg)
L
f
=
Massofice(kg)
Energysupplied(J)
Where:
Energy supplied is the total energy used to melt the ice (in joules).
Mass of ice is the mass of the ice you started with (in kilograms).
Repeat for accuracy:
For more accurate results, repeat the experiment a few times and calculate an average value for the latent heat of fusion.
Safety Considerations:
Ensure the electrical equipment is set up safely to avoid any electric shock.
Handle the ice carefully to avoid slipping.
Conclusion:
By calculating the energy supplied and dividing it by the mass of the ice, you can determine the latent heat of fusion of water. This experiment provides an estimate of the energy needed to melt 1 kg of ice without changing its temperature.
