Fuels

Question 2

Is the enthalpy change for an exothermic reaction positive or negative?

Answer 2

Exothermic reactions have a negative enthalpy change

Question 3

Is the enthalpy change for an endothermic reaction positive or negative?

Answer 3

Endothermic reactions have a positive enthalpy change

Question 4

If the total energy of the products is less than that of the reactants is the reaction exothermic or endothermic?

Answer 4

Exothermic

Question 5

If the total energy of the products is more than the reactants is the reaction exothermic or endothermic?

Answer 5

Endothermic

Question 6

What three things are solution calorimeters used to measure?

Answer 6

Heat of precipitation, heat of solution and heat of neuralisation

Question 7

What is the equation for the calibration factor of a calorimeter?

Answer 7

CF = n x Hc / ∆T
or
CF = E / ∆T
or
CF = VIt / ∆T

Question 8

How do we account for heat loss to the environment when calculating the temperature change to find CF?

Answer 8

By taking recordings of the temperature at regular intervals, the data can be graphed over time and the actual temperature change can be seen in and compared with the final temperature after the mixture was left to cool

Question 9

What units are energy from food in?

Answer 9

kJ /g

Question 10

What are some assumptions made when calculating energy released from food?

Answer 10

The heat of combustion of food assumes we are burning the nutrient in an environment containing excess oxygen. In reality, during digestion the energy value can be less than expected.

Question 11

What is likely to be the difference between the energy released by a food during an experiment where it was burnt, and when the energy released into your body following digestion?

Answer 11

The energy will measure slightly higher during the experiment than during cellular respiration.