4.3- MEASURING ENTHALPY CHANGES

Question 1

What is the general name for the enthalpy change for any reaction?

Answer 1

standard molar enthalpy change of reaction ΔH°

Question 2

What is standard molar enthalpy change of reaction ΔH° measured in?

Answer 2

kilojoules per mole kJmol-1

Question 3

What is the standard molar enthalpy of formation ΔfH°?

Answer 3

enthalpy change when one mole of substance formed from its constituent elements under standard conditions, all reactants + products being in their standard states

Question 4

What is the standard molar enthalpy of combustion ΔcH°?

Answer 4

enthalpy change when one mole of substance completely burnt in oxygen under standard conditions, all reactants + products being in their standard states

Question 5

What is temperature related to?

Answer 5

average kinetic energy of particles in system

Question 6

What happens to average KE and temperature as particles move faster?

Answer 6

average KE increases + temp goes up

Question 7

Does the number of particles present affect temperature?

Answer 7

no

Question 8

What is temperature measured with?

Answer 8

thermometer

Question 9

What is heat a measure of?

Answer 9

total energy of all particles present in given amount of substance

Question 10

What does heat depend on?

Answer 10

how much of substance present

Question 11

What is included in the measure of heat?

Answer 11

energy of every particle

Question 12

Where does heat flow from?

Answer 12

always flows from high to low temp

Question 13

What is the enthalpy change of a reaction?

Answer 13

heat given out / taken in as reaction proceeds

Question 14

Is there an instrument to measure heat directly?

Answer 14

no

Question 15

How can you measure the enthalpy change?

Answer 15

arrange for heat to be transferred into particular mass of substance, often water

Question 16

What three things do you need to know when trying to work out enthalpy change?

Answer 16

mass of substance that’s being heated up/cooled down
temp change
specific heat capacity of substance

Question 17

What is specific heat capacity?

Answer 17

amount of heat needed to raise temperature of 1g of substance by 1K

Question 18

What is the units for specific heat capacity?

Answer 18

Jg-1K-1

Question 19

Enthalpy change equation

Answer 19

q = mcΔT

Question 20

How is a simple calorimeter used?

Answer 20

burn fuel to heat known mass of water + then measure temp rise of water
assume all heat from fuel goes into water

Question 21

What can the simple calorimeter be used to compare?

Answer 21

ΔcH° values of series of similar compounds as errors will be similar for every experiment

Question 22

Is the flame calorimeter better than the simple calorimeter?

Answer 22

yes

Question 23

Why is the flame calorimeter better than the simple calorimeter?

Answer 23

designed to reduce heat loss even further

Question 24

How is the flame calorimeter designed to reduce heat loss even further than the simple calorimeter? (3)

Answer 24

spiral chimney made of copper
flame enclosed
fuel burns in pure oxygen, rather than air

Question 25

How easy is it to measure heat changes for reactions that take place in reactions?

Answer 25

relatively easy

Question 26

How is the heat generated in solutions?

Answer 26

by themselves + only has to be kept in calorimeter

Question 27

What is often used for the calorimeters? (measuring enthalpy change of reactions in solutions)

Answer 27

expanded polystyrene

Question 28

What are expanded polystyrene good at?

Answer 28

good insulators

Question 29

As expanded polystyrene is a good insulator what do they do?

Answer 29

reduce heat loss through their sides

Question 30

What does expanded polystyrene have a low of?

Answer 30

low heat capacity

Question 31

What does it mean as expanded polystyrene has a low heat capacity?

Answer 31

absorb very little heat

Question 32

What is the specific heat capacity of dilute solutions usually taken to be?

Answer 32

same as water- 4.2Jg-1K-1

Question 33

What type of reactions are neutralisation reactions in solution?

Answer 33

exothermic- give out heat

Question 34

General equation for acid neutralised by alkali?

Answer 34

acid + alkali -> salt + water

Question 35

How do you find the enthalpy change for a reaction?

Answer 35

use quantities in moles given by balanced equation

Question 36

When will a metal displace another one from a compound?

Answer 36

when a metal is more reactive than another, it will displace the less reactive one from a compound

Question 37

If a metal that's more reactive than another and displaces the less reactive one in a compound + compound can dissolve in water, how can the reaction be investigated?

Answer 37

using polystyrene beaker

Question 38

What will happen even if expanded polystyrene cups are good insulators?

Answer 38

some heat will still be lost from side + top leading to known values for enthalpy changes measured by this method