Required practical 1: specific heat capacity

What is specific heat capacity

the amount of energy required to raise the temperature of one kilogram of the substance by one degree Celsius.

Specific heat capacity equation

change in thermal energy = mass × speci f ic heat capacity × tem perature change


∆E = m c ∆θ

change in thermal energy, ∆E, in joules, J

mass, m, in kilograms, kg specific heat capacity, c, in joules per kilogram per degree Celsius, J/kg °C temperature change, ∆θ, in degrees Celsius, °C

aim

To determine Fiffick heat capacity of one or more materials

equipment

* 1 kg copper, iron and aluminium metal blocks, each with two holes – one for the heater and one for the thermometer              


* thermometer
* pipette to put water in the thermometer hole
* 30 W heater
* 12 V power supply
* insulation to wrap around the blocks
* ammeter and voltmeter
* 4 mm leads
* stopwatch or stopclock
* balance (capable of measuring more than 1 kg) to determine the mass of the blocks
* heatproof mat.

Method

1. place a beaker on a balance and press 0
2. add oil to beaker and record mass of oil
3. place thrmometer and immersion heater into the oil
4. record the starting temperature of the oil
5. wrap the beaker in insulating foam to reduce thermal energy transfer to the surrounding
6. connect a joulmeter to the immersion heaer
7. leaver for 30 minutes- allow temp to rise enough to accurately read thermometer
8. read number of joules of energy passed into immersion heater
9. read final temp of oil
10. calculate specific heat capacity c = change in thermal energy/ m x change in temp

If a **large amount of energy** is required to heat up a substance what will happen to the specific heat capacity

then its specific heat capacity will be very high. These substances will be able to store lots of energy.

If a **small amount of energy** is required to heat up a substance,what will happen to the specific heat capacity

then its specific heat capacity will be very low. These substances won’t be able to store lots of energy.

Why do you wrap the block in an insulating layer

Reduce the energy transferred from the block to surroundings

Sources if innacuracy

Thermal energy passing out of the beaker into the air- use an insulator with a lower thermal conductivity

Not all thermal energy passing into the oil- ensure that immersion heater is fully submerges

Incorrect reading of thermometer- use an electronic temperature probe

Thermal energy not being spread through liquid- stir liquid

safety precautions

* don’t handle the block or heater whilst or after heating
* keep block on heatproof mat
* take care not to spill water near your power supply- clean up all spills immediately

If the power of the heater being used isn’t given, how can you calculate it?

By connecting it in parallel with a voltmeter, and in series with an ammeter, and then applying the equation: P = I x V

Why do the metal blocks used in the experiment have two holes in them?

One for is for the heater and one is for the thermometer.

What can be done to improve the reading given by the thermometer?

Add a few drops of water in the hole with the thermometer to improve the thermal contact and ensure even heating.

What reading do you record during the experiment and how frequently?

You record the temperature value every 10 minutes from when the heater is inserted and switched on.

What graph do you plot with the data?

A graph of temperature against work done by the heater.

How do you calculate the work done by the heater?

Using the equation: Energy = Power of heater x Time

Once the block has initially warmed up, describe the graph of temperature against work done by the heater that should be obtained.

It should be a linear relationship and so should produce a straight line.

If you start timing from when you switch on the heater, why may the graph not initially be linear?

There will initially be some thermal inertia whilst the block and heater warm up.

What does the gradient of the graph represent?

The inverse of the heat capacity for the metal block.

How do you obtain the specific heat capacity for the metal you are measuring?

Divide the inverse of the gradient by the mass of the metal block used.

What is the difference between heat capacity and specific heat capacity?

Specific heat capacity is the heat capacity measured for a mass of 1 kg.

Why should you wrap insulation around the outside of the metal block?

To reduce the heat loss to the environment and ensure the temperature reading is as accurate as possible.