8. energetics I (as)

Question 1

enthalpy change (delta H) + units

Answer 1

the heat energy change in a reaction at constant pressure
kJ/mol

Question 2

exothermic reaction

Answer 2

give out heat energy
delta H is negative
temp often goes up

Question 3

endothermic reaction

Answer 3

absorb heat energy
Delta H is positive
temperature often falls

Question 4

enthalpy level diagrams show

Answer 4

the overall change of a reaction

Question 5

reaction profile diagrams show

Answer 5

the enthalpy changes during a reaction

Question 6

standard enthalpy change conditions

Answer 6

100kpa
temp 298 kelvins

Question 7

types of standards enthalpy changes

Answer 7

• standard enthalpy change of reaction
• standard enthalpy change of formation
• standard enthalpy change of combustion
• standard enthalpy change of neutralisation

Question 8

standard enthalpy change of reaction def

Answer 8

is the enthalpy change when the reaction occurs in the molar quantities shown in the chemical equation under standard conditions

Question 9

standard enthalpy change of formation

Answer 9

is the enthalpy change when 1 mole of a compound is formed from its elements in their standard states under standard conditions

Question 10

standard enthalpy change of combustion

Answer 10

is the enthalpy change when 1 mole of a substance is completely burned in oxygen under standard conditions

Question 11

standard enthalpy change of neutralisation def

Answer 11

is the enthalpy change when an acid and an alkali react together under standard conditions to form 1 mole of water

Question 12

to find enthalpy change for a reaction you need

Answer 12

number of moles of the stuff that’s reacting
change in temperature of the reaction

Question 13

how can you directly measure the temp change of some reaction mixtures

Answer 13

mix reactants together
stick a thermometer in reaction mixture
measure overall temp change

Question 14

to find enthalpy change of combustion you need a

Answer 14

calorimeter

Question 15

calorimeter is used to

Answer 15

find our how much heat is given out by a reaction by measuring the temp change of some water

Question 16

how to find enthalpy change of combustion of a flammable liquid

Answer 16

• find enthalpy of combustion of a flammable liquid by burning it
• fuel burns heating the water
• measure heat absorbed by the water

Question 17

calculate enthalpy change equation

Answer 17

q = mc changeT

q= heat lost or gained (joules)
m= mass of water or solution (kg)
c= specific heat capacity of water (4.18 J/g/k)
changeT= change in temp of water (k)

Question 18

hess’s law

Answer 18

the total enthalpy change of reaction is always the same no matter which route is taken

Question 19

when reaction happens…

Answer 19

reactant bonds break and products bonds formed

Question 20

bonds breaking is

Answer 20

endothermic
delta H positive
need energy to break bonds

Question 21

bonds formed is

Answer 21

exothermic
delta H negative
energy released

Question 22

bond enthalpy def

Answer 22

amount of energy required to break 1 mole of a type of bond in a molecule in the gas phase

Question 23

mean bond enthalpy def

Answer 23

the energy needed to break one mole of bonds in the gas phase averaged over many different compounds

Question 24

enthalpy change of reaction = equations

Answer 24

sum of bond enthalpies of reactants - sum of bond enthalpies of product

Question 25

standard enthalpy change or atomisation def

Answer 25

when one mole of gaseous atoms is formed from an element in its standard state under standard conditions

Question 26

mean bond enthalpies arrow direction and what’s in the box

Answer 26

downwards gaseous atoms of elements

Question 27

combustion arrow direction and what’s in box

Answer 27

downwards combustion products

Question 28

formation arrows and box

Answer 28

upwards elements in standard state

Question 29

enthalpy of hydration def

Answer 29

enthalpy change of 1 mole of gaseous ion is hydrated and causes no further heat change