Heat Of Combustion

Question 1

Explain the trend in all combustion reactions.

Answer 1

The energy released when the bonds in carbon dioxide and water form must be greater than the energy required to break the bonds in oxygen and the alkanol.

Question 2

How many carbons in propanol?

Answer 2

3

Question 3

How can you improve the accuracy of the experiment in terms of the thermometer?

Answer 3

Using a digital thermometer or a data logger

Question 4

How can you improve the accuracy of the experiment in terms of the distribution of heat in beaker?

Answer 4

Stir the water

Question 5

How can the accuracy be improved in terms of RECORDINGS the temperature.

Answer 5

Ensure that the temperature has stopped rising before recording

Question 6

State 3 assumptions that make the experiment invalid

Answer 6

Assumption that complete combustion occurs, assumption that all heat produced is consumed by the water, assumption that the experiment is taken place under standard lab conditions

Question 7

Is the experiment valid? State why.

Answer 7

No, the experiment is invalid due to the inability to correctly measure the heat of combustion of the alkanol as the aim states due to the given laboratory conditions which are unable to measure heat of combustion within acceptable experimental values.

Question 8

State all the potential hazards of the alkanol a Ethanol and Propanol

Answer 8

Highly flammable
Volatile
Slightly toxic
Reacts with oxidants
Reacts with alkali metals to form explosive hydrogen gas
Skin and eye irritant

Question 9

Methanol is equally as hazardous as both ethanol and propanol although is considered to have another hazard which the two do not specifically have; state this hazard.

Answer 9

Especially toxic, can lead to permanent blindness if ingested

Question 10

How many kJ is one J

Answer 10

1000

Question 11

How can you improve the validity of the experiment?

Answer 11

Ensure the wick is teased out before it is burnt
Put flame just below the flask/beaker of water
Ensure that the temperature stops rising before it is recorded
Put boxes around the flame to avoid the loss of heat

Question 12

State the controlled variables of the experiment

Answer 12

The volume/mass of water heated
The contained used to heat the water
The difference in temperature
The distance of the flame to the flask
The height of the flame 
The amount of wick teased out

Question 13

State the dependent variable of the experiment

Answer 13

The mass of alkanol burnt

Question 14

State the independent variable (what you change)

Answer 14

The type of alkanol used

Question 15

Are ALL combustion reactions endothermic or exothermic?

Answer 15

Exothermic