chemical change

Question 1

why does increasing the surface area increase the rate of reaction

Answer 1

• if one of the reactants is a solid, breaking it up increases the surface area to volume ratio
• same volume of solid, articles will have more room, so more collisions

Question 2

why does using a catalyst increase the rate of reaction

Answer 2

• provides alternate reactive pathway with lower activation energy
• increases rate of reaction

Question 3

what is the equation for a rate of a reaction?

Answer 3

amount used/ formed / time

Question 4

when the product is a gas:

Answer 4

measured in cm^3

Question 5

when the product is a solid:

Answer 5

grams

Question 6

time

Answer 6

seconds

Question 7

what are the 3 ways of measuring the rate of a reaction?

Answer 7

• precipitation and colour change
• change is mass and gas given off
• volume of gas given off

Question 8

explain precipitation and colour change

Answer 8

• solution is transparent and solution becomes opaque
• reactants are coloured and products are colourless or vice versa
• can’t plot a graph b its subjective

Question 9

explain change in mass and gas given off

Answer 9

• use a mass balance
• quicker reading drops faster reaction bc as gas is given off the mass reduces
• take measurements at regular intervals and plot a graph
• most accurate but releases gas into room

Question 10

explain volume of gas given off

Answer 10

• use gas syringe
• more given off the faster the reaction
• take measurements at regular intervals and plot graph
• if reaction is too vigorous, can blow plunger out of the end of the syringe

Question 11

how do you work out the mean rate of a reaction?

Answer 11

y2 coordinate - y1 coordinate / difference in time

Question 12

how do you work out the rate of a reaction?

Answer 12

draw a tangent and find the gradient of the tangent

Question 13

explain a reversible reaction

Answer 13

• react and concentrations fall, so forward slows down
• more products made concentration rise, backward speeds up
• equilibrium closed system no overall effect means reached balance and wont change

Question 14

what 3 things effect equilibrium

Answer 14

• temperature
• pressure (gas)
• concentration

Question 15

what is le chatelier’s principle?

Answer 15

if you change the conditions of a reversible reaction at equilibrium, the system will try to counteract the change

Question 16

what are hydrocarbons

Answer 16

the simplest organic compounds

Question 17

what are the simplest types of hydrocarbons you can get and what is their formula?

Answer 17

• alkanes

- cn h2n+2

Question 18

what pattern do the carbons go in?

Answer 18

1, 2, 3 ,4

Question 19

what pattern do the hydrogens go in?

Answer 19

4, 6, 8, 10

Question 20

what happens to the hydrocarbons the length of the chain?

Answer 20

• short = less viscous
• short = more volatile
• short = more flammable

Question 21

what is the equation for complete combustion of hydrocarbons?

Answer 21

hydrogen + carbon = carbon dioxide + water

Question 22

what are hydrocarbons used for?

Answer 22

fuels because of the amount of energy released when they combust completely

Question 23

what are the chemical symbols of hydrocarbon, oxygen, water and carbon dioxide?

Answer 23

• CH4
• O2
• H2O
• CO2

Question 24

what is crude oil?

Answer 24

• fossil fuel
• dead plankton millions of years old buried in mud
• high temp and pressure turns to crude oil which can be drilled up from rocks where its found

Question 25

how are hydrocarbons separated?

Answer 25

- mixture of different hydrocarbons, most of which are alkanes - separated using fractional distillation

Question 26

how does fractional distillation work?

Answer 26

- heated until gas - enter fractionating column with temp gradient - long hc - high bp, short hc - low bp - end up separating

Question 27

how is oil used in daily life?

Answer 27

- fuel | - petrochemical industry

Question 28

what are alkenes?

Answer 28

more reactive starting material used to make polymers

Question 29

what is cracking?

Answer 29

thermal decomposition reaction

Question 30

what are the different methods of cracking?

Answer 30

- heat long chain hydrocarbons to vaporise - vapour pass over hot powered aluminium catalyst - long chain split apart on surface of specks of catalyst (catalytic cracking) - or mix with steam then heat (steam cracking)

Question 31

give two examples of pure substances and define pure substances

Answer 31

pure milk and beeswax and when nothing has been added to it and it's in its natural state and contains one compound or element.

Question 32

how do you test the purity of a sample?

Answer 32

by measuring its melting or boiling point and comparing it with that of pure substances found in a data book

Question 33

what will impurities do to your measurements?

Answer 33

lower mp and increase melting range of substance and increase bp and resluts in sample boining over a range of temperatures

Question 34

what are formulations?

Answer 34

usefulmixtures with a precise purposemade by following a formula. each component is measured and contributes to the properties of it so that it meets its required function

Question 35

what are paints formulations composed of?

Answer 35

- pigment (colour) - solvent (dissolve other components and alter viscosity) - binder (holds the pigment in place) - additives (change other properties of the paint)

Question 36

how do you test for chlorine?

Answer 36

bleaches damp litmus paper white because it's acidic

Question 37

how do you test for oxygen?

Answer 37

glowing splint inside test tube containing oxygen the oxgen will relight

Question 38

how do you test for carbon dioxide?

Answer 38

bubbling co2 through limewater turns it cloudy

Question 39

how do you test for hydrogen?

Answer 39

hold a burning splint open at a test tube of hydrogen and you'll hear a squeaky pop

Question 40

what is chromatography?

Answer 40

method used to separate substances in a mixture

Question 41

what is the mobile phase?

Answer 41

the solvent - liquid or gas as the molecules can move

Question 42

what is the stationary phase?

Answer 42

the paper - molecules can't move as it's a solid

Question 43

how do you calculate Rf values?

Answer 43

distance travelled by substance / distance travelled by solvent