Chapter 6

Question 1

% yield

Answer 1

actual yield/EXPECTED YIELD X 100

Question 2

purity %

Answer 2

mass of pure product / mass of impure product x100

Question 3

endothermic

Answer 3

gains energy, absorbs

Question 4

exothermic

Answer 4

gives off, exserted, lost

Question 5

combustion reaction

Answer 5

combustion of fossil fuels gas and oil = exothermic
fossil fuels are so useful because:
-they can be easily ignited and burnt
-they are capable of releasing large amounts of energy as heat

Question 6

examples of exothermic reactions

Answer 6

photosynthesis,thermal decomposition of limestone

Question 7

heat of reaction

Answer 7

-the energy change from reactants to product in a chemical reaction
-heat of reaction = delta aitch - triangle symbol
unit of heat change = kj (kilojoules)
1kj = 1000j
-calculation per mole of compound = kj/mol

Question 8

breaking and making bonds

Answer 8

heat energy triangle H = heat energy = energy difference

-triangle H = energy required to break bonds - energy required to form bonds

Question 9

catalyst

Answer 9

haber process =IRON
contact process= Vanadium oxide
hydrogenation of fats =Nickel
oxidation of NH3 =Platinum - Rhadium
alcoholic drinks industry=Enzymes (yeast)
conversion of methanol to hydrocarbons = Zeolite

Question 10

heat of combustion

Answer 10

is the change of a reaction when a substance is burnt

Question 11

usage of a metal calorimetry

Answer 11

how to measure heat of combustion *how much is lost

-insulator to not lose heat to surroundings

Question 12

rate of reaction

Answer 12

speed = distance / time = km/hr -

-how concentrations of reaction changes over time = rate of reaction

Question 13

factors affecting rate of reaction

Answer 13

1. surface area of solid reactants
2. concentration
3. temp
4. catalyst
5. light on some reactions

Question 14

surface area

Answer 14

increase = quicker rate of reaction

Question 15

concentration

Answer 15

increase = faster rate of reaction = more molecules of reactants in solution

Question 16

temp

Answer 16

increase = rate of reaction increases = kinetic energy = more collisions

Question 17

catalyst

Answer 17

: substance that speeds up the rate of chemical reaction and is unchanged at the end

eg: decomposition of hydrogen peroxide = h2o2 =2h2o + o2
at room temp reaction is very slow
manganse (iv) oxide = MnO2 is used as a catalyst

Question 18

catalyst converter

Answer 18

is a device for converting polluting exhaust gases from cars into less dangerous emissions

= removes polluting oxides and completes oxidation of unburnt hydrocarbon fuels

Question 19

honey combed surface

Answer 19

converter contains a thin coating of rhadium and platium catalyst on a solid honeycombed surface

Question 20

biological catalysts

Answer 20

protein molecules called enzyme -living cells also produce enzymes

they are specific
sensitive to temp *above 45 degrees, denatured and inactive
senitive to pH (7)

these catalyst are used to make washing soup/powders - removes blood, stains ,sweat 30-40 degrees

Question 21

solid catalyst

Answer 21

different reactions need different catalysts

• one broad groupf of catalysts work on absorbing molecules on to the solid surface (BRINGS MOLECULES OF REACTANTS CLOSER)
• it is also thought the process of absorption weaken bonds in reactants molecules = this increases frequency of collision and molecules likely to react

Question 22

activation energy

Answer 22

-energy required to start a chemical reaction
for reaction to take place=colliding partials must posses at least this amount of energy
-all reactions have activation energy = minimum energy required by reactants to from products

-catalysts increases rate of reaction by reducing energy required to break bonds

Question 23

biomass

Answer 23

the energy stored directly by plants through photosynthesis

• provides food and warmth
• can be changed into fossil fuels by heat and pressure

Question 24

respiration

Answer 24

c6h1206 + 6o2 = 6co2 + 6h2o

Question 25

photography

Answer 25

2agbr = 2ag + br2

bromide ions are oxidised and silver ions are reduced

• this photochemical reactions, in which silver ions are converted to silver atoms, is used s the basis of black and white and colour photography

Question 26

Photochemical reaction

Answer 26

the photographic film itself is simply a flexible plastic support for the light sensitive emulsion

• a emulsion in a photgraphy is not true emulsion but a layer or gelatine which millions of microcrystals of silver bromide spread through it.
• black and white has a single layer
• colour film has three layers each containing different dyes