Enthalpy&measuring change

Question 1

What is enthalpy change?

Answer 1

The heat transferred in a reaction at a constant pressure

Question 2

What are units of enthalpy change?

Answer 2

kJ mol -1

Question 3

What are standard conditions?

Answer 3

100kPa

Stated temp usually 298K

Question 4

What is an exothermic reaction?

Answer 4

energy given out to surroundings, temperature goes up

Question 5

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

Answer 5

Negative

Question 6

What is an example of an exothermic reaction?

Answer 6

Combustion

Question 7

What is an endothermic reaction?

Answer 7

energy taken in from surroundings, temperature falls

Question 8

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

Answer 8

Positive

Question 9

What technique is used to measure enthalpy change?

Answer 9

Calorimetry

Question 10

How does calorimetry work to measure enthalpy change?

Answer 10

As the fuel burns, it heats the water and you can work out how much energy has been absorbed by the water if you know the mass, the temperature change and the specific heat capacity

Question 11

What two equations do you need to work out enthalpy change?

Answer 11

q=m x c x Δt

ΔH= q/n

Question 12

What is mass measured in?

Answer 12

g

Question 13

What is temperature measured in?

Answer 13

K

Question 14

What is the specific heat capacity?

Answer 14

4.18 j g-1 K-1

Question 15

What is ‘q’ in the equation?

Answer 15

Heat lost or gained in joules

Question 16

How do you convert q from joules into kilojoules?

Answer 16

divide by 1000

Question 17

What do you divide q by?

Answer 17

the number of moles of the fuel that caused the enthalpy change

Question 18

How do you calculate the number of moles?

Answer 18

Moles = Mass/Mr

Question 19

What would you put in front of the answer for enthalpy change if the temperature has gone up?

Answer 19

Negative symbol as it is an exothermic reaction

Question 20

What would you put in front of the answer for enthalpy change if the temperature has gone down?

Answer 20

Postive symbol as it is an endothermic reaction

Question 21

What are some experimental problems with calorimetry?

Answer 21

• some heat absorbed by container

- some heat lost to surroundings

Question 22

What are some experimental problems which only apply to flammable liquid calorimetry?

Answer 22

• Some combustion may be incomplete - less energy given out

- Some flammable liquid may escape by evaporation