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Question 1

what are exothermic reactions

Answer 1

reactions that give out heat as the reactants change to products so the temp changes

Question 2

what are endothermic reactions

Answer 2

reactions that take in heat as reactants change to products so the temp drops

Question 3

what is enthalpy change

Answer 3

heat energy change measured under a constant pressure

Question 4

what are standard conditions

Answer 4

100KPa

298K

Question 5

what is the standard state of an element

Answer 5

physical state under standard conditions

Question 6

what is the definition of standard enthalpy change of combustion

Answer 6

the enthalpy change when one mole of substance is completely burned in oxygen under standard conditions, with all reactants and products in their standard states

Question 7

what does standard enthalpy change refer to

Answer 7

heat change measured at 100KPa and 298K

Question 8

what is the definition of standard enthalpy change of formation

Answer 8

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

Question 9

what equation would you use to calculate the heat change for a reaction

Answer 9

Q=Mc > T

Question 10

what is Hess’s Law

Answer 10

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

Question 11

how is an enthalpy change different from a heat change

Answer 11

an enthalpy change is an energy change measured under a stated temp and constant stated pressure

Question 12

what is the unit of energy

Answer 12

Joules

Question 13

what is the most stable form of Carbon, and what state symbol is it given

Answer 13

Graphite (s)

Question 14

what value is given to deltaH of elements

Answer 14

zero, no energy is needed to form an element from its element

Question 15

why will the value calculated for an enthalpy change be different using mean bond enthalpies compared to thermochemical cycles

Answer 15

mean bond enthalpies are averages, and the true value will differ. thermochemical cycle is ‘correct’ answer

Question 16

are mean bond angels positive or negative? why?

Answer 16

Positive because energy must be put in to break bonds

Question 17

when drawing enthalpy diagrams, what do we take as 0

Answer 17

elements

Question 18

what Is meant by the bond dissociation enthalpy

Answer 18

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

Question 19

what is the difference between heat and temp.

Answer 19

temp- average kinetic energy of the particles in a system

heat- total amount of energy of all particles present

Question 20

do endothermic reactions have positive or negative values

Answer 20

positive

Question 21

explain the trend in electronegativity that we see in the halogens

Answer 21

halogens become more electronegative as we move up the group because the distance between the nucleus and the bonding electrons decreases, so does shielding

Question 22

what sort of agents are halide ions

Answer 22

reducing agents

Question 23

what happens to the ability of halide

ions to act as reducing agents as we move down the group? why?

Answer 23

increases because more shielding and size of atom means outer elecrons are less strongly attracted to the nucleus and so are easily lost

Question 24

why is the reaction of sodium bromide with concentrated sulphuric acid different from the reaction of sodium chloride with it

Answer 24

bromide ions are stronger reducing agents than chloride ions so are able to reduce the sulphuric acid to sulphur dioxide

Question 25

how can we predict if one halogen will displace another halogen ion

Answer 25

a halogen will displace the ion of a halogen that is below it in the periodic table

Question 26

explain the trend in boiling point that we see in the halogens

Answer 26

Bp increases as we move down the group. because larger atoms have more electrons an so stringer van der waals forces between molecules

Question 27

how do halogens normally react

Answer 27

by gaining electrons

Question 28

what sort of agent are halogens

Answer 28

oxidising

Question 29

what happens to the ability of halogens to act as oxidising agents as we move down the group? why?

Answer 29

decreases because increased shielding and size of atom means electrons are less strongly attracted to the nucleus

Question 30

why are the products from the reaction of NaBr with conc H2SO4 different from Nal?

Answer 30

iodide ions are stronger reducing agents than bromide ions, so reduce the sulphur further

Question 31

what reagent would you use to distinguish between halide ions

Answer 31

Acidified silver nitrate

Question 32

what acid would you chose to acidify silver nitrate

Answer 32

nitric acid

Question 33

why do we acidify silver nitrate before testing halogen ions

Answer 33

to remove ions that would form precipitates and interfere with results eg carbonate

Question 34

what colour precipitates are formed when halide ions react with acidified silver nitrate

Answer 34

AgF- none
AgCL- white
AgBr- cream
AgI- yellow

Question 35

what is the trend in solubility of the silver halides as we move down the group

Answer 35

becomes less soluble
AgCl- dissolves in dilute ammonia
AgBr- dissolves in conc. ammonia
AgI- insoluble in conc. ammonia

Question 36

what do we call a reaction in which an element is both oxidised and reduced

Answer 36

disproportionation

Question 37

what is the formula of chloric(1) acid

Answer 37

HClO

Question 38

why is chlorine added to water

Answer 38

it produces chloric (1) acid which kills bacteria by oxidation and is also a bleach

Question 39

what is the formula of sodium chlorate? what are the oxidation numbers if the elements in it

Answer 39

NAClO-
NA +1
Cl +1
O -2