Calorimetry - Calorimeters Introduction

Question 1

What is a Calorimeter used for?

Answer 1

The measurement of Enthalpy/Heat Content

Question 2

What are the 2 types of Calorimeters

Answer 2

1. Solution (simple) Calorimeter
2. Bomb Calorimeter

Question 3

What does a Calorimeter measure in the experiment?

Answer 3

The change in temperature that occurs during a reaction

This value can be used to find enthalpy

Question 4

Each Calorimeter has its own calibration factor. What is a Calibration factor?

Answer 4

Calibration factor is the energy required to change the temperature within calorimeter by 1 °C. It is determined experimentally.

Question 5

What does a Solution (simple) calorimeter like?

Answer 5

• A vessel with known amount of water.
• Container is insulated (prevents heat loss to surroundings)
• Has a stirrer (keeps temprature constant throughout vessel)
• Thermometer (record temperature changes)

Refer to diagram online

Reactants are placed iwthin solution for solution calorimeter

Question 6

What is the purpose of a Bomb Calorimeter (how is it special)?

Answer 6

Allows for the determination of enthalpies for Combustion reactions, fuels and foods.
Reactants are not placed within solution.

Question 7

What does a Bomb Calorimeter look like?

Answer 7

More spohisticated equipment:
* Reactants placed inside a ‘bomb’ where they are ignited
* Bomb is surrounded by water (where temperature change occurs)
* Water’s vessel is insulated
* Ignition coil placed in reactants and wires stick out of calorimeter to initiate ignition
* Thermometer and stirrer in water

Refer to diagram online

Question 8

The measurement of enthalpy of substances can be found using a calorimeter. State the two methods of finding it:

Answer 8

1. Calibration Factor Method
2. Specific Heat Capacity Method

Question 9

What are the two types of Calibration Methods?

Answer 9

1. Electrical calibration
2. Chemical calibration

Question 10

What data needs to be known for conducting the Calibration Method for finding enthalpy?

Answer 10

1. Calibration Factor (alternatively need to know amount of volts, amps, duration and ΔT)
2. ΔT
3. Mass of tested substance

Question 11

Give equation for Electrical Calibration

Answer 11

Cf = (VxIxT) / ΔT

V = volts, I = amps, T = time/duration, ΔT = difference in temperature

Question 12

Describe process of conducting an electrical calibration

Answer 12

1. A known voltage and current is applied through a heating coil for a specific time
2. Heating coil heats up water/solution
3. Temperature change within this time is recorded

Electrical Calibration is used for Solution (simple) calorimeters

Question 13

Why is chemical calibration used?

Answer 13

As bomb calorimeters usually require chemical calibration as eletrical calibration cannot be conducted on them

However, VCAA is known to use electrical calibration on bomb calorimeter

Question 14

What chemical is used usually for chemical calibration and why?

Answer 14

Benzoic acid is usually used - it has a very accurately known enthalpy

May be asked to work out calibraton factor of bomb calorimeter using chemical calibration - all data for calculations will be provided though

Question 15

What’s formula for finding enthalpy with known Calibration factor and ΔT?

Answer 15

Heat energy evolved = ΔT x Calibration Factor

E = ΔT x Cf

Question 16

Explain the 3 steps for finding enthalpy using Calibration Factor

Answer 16

1) Calibrate Calorimeter
* Set V, I and t
* Record ΔT
* Use Cf = (VIt)/ΔT to find calibration factor

2) Complete reaction and record ΔT
* Use E = Cf x ΔT to get energy evolved

3) Find ΔH
* Energy evolved is for ‘x’ amount of grams
* Convert grams to moles
* Then divide by number of moles to get ΔH

Question 17

What data needs to be known for conducting the specfic heat capacity method for finding enthalpy?

Answer 17

1. Mass of water (or other solution)
2. Specific heat capacity of water (or other solution)
3. ΔT
4. Mass of tested substance

Question 18

What is the equation for finding energy evolved using specific heat capacity?

Answer 18

Energy (J) = Specifc Heat Capacity x Mass of water (g) x ΔT (degrees C)

E = Cp x m(H2O) x ΔT

Question 19

What are the 2 steps in finding enthalpy using specific heat capacity method?

Answer 19

1) Find energy inputted into water by substance
* E = Cp x mass(H2O) x ΔT

2) Find ΔH
* Energy found in step 1 if for ‘x’ amount of grams
* Convert grams to moles
* Divide energy by number of moles for ΔH

Question 20

Why might specific heat capacity method be used instead of calibration factor method?

Answer 20

1. When amount of water is known
2. When Calibration factor is undeterminable

Question 21

When might enthalpy found using calorimeters not be given per mole, but per gram instead?

Answer 21

When tested substance is a mixture

Question 22

For solids and liquids how do you convert kJ/mol to kJ/g?

Answer 22

Divide by M (molar mass)

Question 23

For solids and liquids how do you convert kJ/gram to kJ/mol

Answer 23

Multiply by M (molar mass)

Question 24

For gasses how do you convert kJ/mol to kJ/gram

Answer 24

Divide by Vm (molar volume of an ideal gas at SLC)

Question 25

For gasses how do you convert kJ/gram to kJ/mol

Answer 25

Multiply by Vm (molar volume of an ideal gas at SLC)