CC13,14,15 - rates, energy, groups and heat changes Flashcards
what are group 1 elements known as?
alkali metals
properties of group 1
one electron in the outer shell
low melting and boiling points
very soft
low density
form ionic compounds
why do group 1 elements get more reactive going down the group?
- atomic radius gets larger
- less electrostatic attration between nucleus and outermost electron
- outermost electron is more easily lost (to gain a full outer shell)
what happens when group 1 is reacted with water?
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
saftey regarding reacting group 1 with water
- 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
what are group 7 known as?
halogens
properties of halogens?
- 7 electrons in outer shell
- diatomic, share electrons in a covalent bond
- melting and bp increase going down group
- more reactive going up group
describe state and colour of halogens at room temp?
Flourine- gas- pale yellow
chlorine- gas- green
bromine - liquid- red/ brown
iodine- grey- soild
explain state of group 7 elements
intermolecular forces of attraction get stronger going down the group therefore boiling and melting point increase.
how to test for chlorine
hold damp blue litmus paper over it, chlorine will bleach it red then white as chlorine is acidic
why does reactivity of group 7 decrease going down the group
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
explain displacement
more reactive halogens displace less reactive halogens
what is a hydrogen halide
hydrogen and a halogen, when dissolved in water it always forms an acid
what is a redox reaction?
reduction - gain of electrons
oxidation - loss of electrons
(when both happen)
OIL RIG
what are group 0 elements known as?
noble gases
properties of group 0
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
what needs to happen in order for particles to react?
collide with enough energy
what are reactants?
variables that react
what are products?
variables that are made
ways to speed up a reaction?
- increase acid concentration
- increase surface area
- increase temperature
- use a catlyst
how does increasing temp speed up a reaction?
particles gain more energy and they can move faster, they collide more often and harder.
how does increasing acid concentration speed up a reaction?
particles remain w same energy and at same speed but there are more particles per cm3 therefore collisions are more likley and frequent.
how does increasing SA speed up a reaction?
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.
what is activation energy?
the energy required to break bonds between atoms in reactant molecules
what is a catalyst?
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
what is exothermic?
gives out energy
what is endothermic?
takes energy in
what is a 2 stage reaction?
stage 1: break bonds (endo)
stage 2: make new bonds (exo)
how do catalysts speed up a reaction?
- provides a different pathway with a lower activation energy
- more particles exceed this activation energy and undertake successful collisions
- catalyst increases rate of reaction
what do catalytic converters do?
reduce pollution by turning harmful gases into less harmful gases
why must catalyst be spread thinly over a honeycomb in a catalytic converter?
higer SA - more collisions
What is a reagent
a substance or compound added to a system to cause a chemical reaction, or test if one occurs
Examples of exothermic reactions
- displacement reactions
- precipitation reactions
- most neutralisation reactions
Examples of endothermic reactions
- Ethanoic acid and sodium carbonate
- dissolving ammonium chloride
How to calculate overall energy change
Energy required to break bonds - energy released when new bonds are formed
What does a positive energy change mean
An endothermic reaction
What does a negative energy change mean
An exothermic reaction
