Measuring enthalpy changes

Question 1

What does the Kelvin scale of temperature start at?

Answer 1

Absolute zero

Question 2

What is the value of absolute zero?

Answer 2

0K (-273 oc)

Question 3

What temperature does ice melt at on the Kelvin scale?

Answer 3

273K (0 oc)

Question 4

What temperature does water boil at on the Kelvin scale?

Answer 4

373K (100 oc)

Question 5

What is a 1K rise in temperature equal to?

Answer 5

1 oc rise in temperature

Question 6

What are the three quantities used to calculate energy change of the surroundings?

Answer 6

1) Mass
2) Specific heat capacity
3) Temperature change

Question 7

What is mass measured in?

Answer 7

Grams (g)

Question 8

What is the symbol for mass?

Answer 8

m

Question 9

What is specific heat capacity?

Answer 9

The energy required to raise the temperature of 1g of a substance by 1K

Question 10

What is the symbol for specific heat capacity?

Answer 10

c

Question 11

What materials have small values of c?

Answer 11

Good conductors of heat, e.g. metals

Question 12

What materials have large values of c?

Answer 12

Insulators of heat, e.g. foam plastic

Question 13

What is the value of c for water?

Answer 13

4.18 J g-1 K-1

Question 14

What is the symbol for temperature change?

Answer 14

▲T

Question 15

What is the formula for temperature change?

Answer 15

▲T = T (final) - T (initial)

Question 16

What is the symbol for heat energy?

Answer 16

q

Question 17

What is the equation for calculating energy change?

Answer 17

q = mc▲T

Question 18

What is combustion?

Answer 18

A reaction of a substance with oxygen

Question 19

What is the symbol for enthalpy change of combustion?

Answer 19

▲cH

Question 20

What are the three steps to calculate enthalpy change of combustion?

Answer 20

1) Calculate the energy change q of water in kJ
2) Calculate the amount, in mol, of the substance burnt
3) Calculate ▲cH in kJ mol-1

Question 21

How accurate is the experimental ▲cH value?

Answer 21

Data book values are higher than experimental values showing that experimental values are less exothermic than expected

Question 22

What are the four reasons for why experimental values are less accurate?

Answer 22

1) Heat loss to surrounding other than water
2) Incomplete combustion, where carbon monoxide and carbon are produced instead of carbon dioxide (black layer)
3) Evaporation of the substance from the wick after extinguishing the flame
4) Non-standard conditions

Question 23

What is the symbol for enthalpy change of reaction?

Answer 23

▲rH

Question 24

What can be used to measure enthalpy change of reaction?

Answer 24

A plastic cup made of polystyrene foam

Question 25

Why does temperature change occur in reactions?

Answer 25

The chemical particles within the solutions may react when they collide, and any energy transfer between the chemical particles and water molecules in the solution results in temperature change

Question 26

What is placed in the cup to record temperature change?

Answer 26

A thermometer

Question 27

What is the formula for calculating heat energy?

Answer 27

mc▲T

Question 28

What are the three steps to calculate enthalpy change of reaction?

Answer 28

1) Calculate the energy change q in the solution in kJ
2) Calculate the amount, in mol, of the solution that reacted
3) Calculate ▲rH in kJ mol-1

Question 29

What is the symbol for enthalpy change of neutralisation?

Answer 29

▲neutH

Question 30

How is enthalpy change of neutralisation different from enthalpy change of reaction?

Answer 30

Two solutions react, rather than a solution and a solid

Question 31

What are the three steps to calculate enthalpy change of neutralisation?

Answer 31

1) Calculate the energy change q in the solution in kJ
2) Calculate the amount, in mol, of both solutions that reacted
3) Calculate ▲neutH in kJ mol-1