CC13,14,15 - rates, energy, groups and heat changes

Question 1

what are group 1 elements known as?

Answer 1

alkali metals

Question 2

properties of group 1

Answer 2

one electron in the outer shell
low melting and boiling points
very soft
low density
form ionic compounds

Question 3

why do group 1 elements get more reactive going down the group?

Answer 3

• atomic radius gets larger
• less electrostatic attration between nucleus and outermost electron
• outermost electron is more easily lost (to gain a full outer shell)

Question 4

what happens when group 1 is reacted with water?

Answer 4

reacts vigorously producing hydrogen gas and a hydroxide of the metal
Li, Na, K - move around surface + fizz
K - ignites
Na, K - can melt in the heat of the reaction

Question 5

saftey regarding reacting group 1 with water

Answer 5

• gloves, goggles, lab coat - protects eyes and clothing , prevents metals reacting w moisture on hands
• behind screen
• stand away (spitting)
• dont touch metal
• put everything in water to react unreacted metal at end
• small amount of metal

Question 6

what are group 7 known as?

Answer 6

halogens

Question 7

properties of halogens?

Answer 7

• 7 electrons in outer shell
• diatomic, share electrons in a covalent bond
• melting and bp increase going down group
• more reactive going up group

Question 8

describe state and colour of halogens at room temp?

Answer 8

Flourine- gas- pale yellow
chlorine- gas- green
bromine - liquid- red/ brown
iodine- grey- soild

Question 9

explain state of group 7 elements

Answer 9

intermolecular forces of attraction get stronger going down the group therefore boiling and melting point increase.

Question 10

how to test for chlorine

Answer 10

hold damp blue litmus paper over it, chlorine will bleach it red then white as chlorine is acidic

Question 11

why does reactivity of group 7 decrease going down the group

Answer 11

need to gain 1 electron for a full outer shell, it is harder for elements further down the group to attract the electron as the outer shell is further from the nucleus therefore theyre less reactive

Question 12

explain displacement

Answer 12

more reactive halogens displace less reactive halogens

Question 13

what is a hydrogen halide

Answer 13

hydrogen and a halogen, when dissolved in water it always forms an acid

Question 14

what is a redox reaction?

Answer 14

reduction - gain of electrons
oxidation - loss of electrons
(when both happen)
OIL RIG

Question 15

what are group 0 elements known as?

Answer 15

noble gases

Question 16

properties of group 0

Answer 16

inert - unreactive, already have a full outer shell of electrons
all gases
bp increases going down group as they get bigger and heavier
density increases going down

Question 17

what needs to happen in order for particles to react?

Answer 17

collide with enough energy

Question 18

what are reactants?

Answer 18

variables that react

Question 19

what are products?

Answer 19

variables that are made

Question 20

ways to speed up a reaction?

Answer 20

• increase acid concentration
• increase surface area
• increase temperature
• use a catlyst

Question 21

how does increasing temp speed up a reaction?

Answer 21

particles gain more energy and they can move faster, they collide more often and harder.

Question 22

how does increasing acid concentration speed up a reaction?

Answer 22

particles remain w same energy and at same speed but there are more particles per cm3 therefore collisions are more likley and frequent.

Question 23

how does increasing SA speed up a reaction?

Answer 23

particles will only collide with the outside of a variable, cant get to the middle. if it is in smaller peices, particles have more area to collide with and there are more collisions per second.

Question 24

what is activation energy?

Answer 24

the energy required to break bonds between atoms in reactant molecules

Question 25

what is a catalyst?

Answer 25

a substance that speeds up a reaction by lowering the activation energy. doesnt get used up so it can be reused - only a small amount is needed

Question 26

what is exothermic?

Answer 26

gives out energy

Question 27

what is endothermic?

Answer 27

takes energy in

Question 28

what is a 2 stage reaction?

Answer 28

stage 1: break bonds (endo)
stage 2: make new bonds (exo)

Question 29

how do catalysts speed up a reaction?

Answer 29

• provides a different pathway with a lower activation energy
• more particles exceed this activation energy and undertake successful collisions
• catalyst increases rate of reaction

Question 30

what do catalytic converters do?

Answer 30

reduce pollution by turning harmful gases into less harmful gases

Question 31

why must catalyst be spread thinly over a honeycomb in a catalytic converter?

Answer 31

higer SA - more collisions

Question 32

What is a reagent

Answer 32

a substance or compound added to a system to cause a chemical reaction, or test if one occurs

Question 33

Examples of exothermic reactions

Answer 33

• displacement reactions
• precipitation reactions
• most neutralisation reactions

Question 34

Examples of endothermic reactions

Answer 34

• Ethanoic acid and sodium carbonate
• dissolving ammonium chloride

Question 35

How to calculate overall energy change

Answer 35

Energy required to break bonds - energy released when new bonds are formed

Question 36

What does a positive energy change mean

Answer 36

An endothermic reaction

Question 37

What does a negative energy change mean

Answer 37

An exothermic reaction