Energetics

Question 1

Enthalpy change

Answer 1

The heat energy change measured under constant pressure whilst temperature depends on the average kinetic energy of the particles

Question 2

calculating enthalpy change

Answer 2

q=m x c x T

Question 3

Standard conditions

Answer 3

Pressure= 100kPa
Temperature= 298K

Question 4

Standard enthalpy of formation

Answer 4

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

Question 5

Standard enthalpy of combustion

Answer 5

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

Question 6

Specific heat capacity

Answer 6

The amount of heat needed to raise the temperature of 1g of substance by 1K, measured in joules per gram per kelvin

Question 7

Calorimeter

Answer 7

The apparatus used to measure the heat changes in chemical reactions

Question 8

Hess’ Law

Answer 8

The enthalpy change for a chemical reaction is the same, whatever route is taken from reactants to products

Question 9

Bond dissociation enthalpy

Answer 9

The enthalpy change required to break a covalent bond with all species in the gaseous state

Question 10

Mean bond enthalpy

Answer 10

The average value of the bond dissociation enthalpy for a given type of bond taken from a range of different compounds

Question 11

practical

Answer 11

polystyrene cup

Question 12

what reactions is this used practical for

Answer 12

• acid + metal
• acid + metal carbonate
• displacement of metals
• neutralisation

Question 13

what are the steps for the polystyrene cup practical

Answer 13

1)put polystyrene cup in beaker
2) in cup put 25 cm cubed of acid using a measuring cylinder
3)put thermometer in acid and measure starting temp until min 4
4)put 5g of solid sample in acid on min 4 and stir
5)measure temperature every min for 10 min and record higherst temp reached
6) calculate change in temperature
7)repeat two more times and calculate a mean temp change, discarding any anonymily results
8)repeat for each sample
9)the sample with the highest temperature change is the most reactive metal.

Question 14

what can you do to reduce heat loss

Answer 14

put a lid on the polystyrene cup

Question 15

exothermic reaction profiles

Answer 15

reactants energy higher then products

Question 16

endothermic reaction profiles

Answer 16

energy of reactants lower then that of the products