Topic 7 - Groups In The Periodic Table, Rate Of Reaction, Energy Changes In Chemical Reactions Flashcards
spectator ion
an ion that doesn’t change during a chemical reaction
activation energy
minimum energy with which particles must collide in order to cause a chemical reaction
neutralisation reaction - what does it form
is when an acid and a base react to form water and a salt
how is the periodic table arranged
so that elements in the same vertical column (group) have similar chemical properties
what elements are in group 1
the alkali metals
alkali metal properties
- low melting and boiling points
- soft
- easily cut
- low density
- very reactive
- readily form compounds with non-metals
What non-metals do alkali metals react with
- oxygen
- chlorine
- water
how does the reactivity differ in group 1
it increases as you go down the group
what are the two products in an alkali metal + a non metal reaction
metal hydroxide + hydrogen
observations: what happens when you react an alkali metal with water and how does the reactivity change as you go down the group
as you go down the group:
it starts bubbling then it fizzes about on the surface then it bursts into flames
explain the trend of reactivity in group 1 using electron configuration
- group 1 atoms loose one electron when they react
- as you go down group 1, an electron shell is being added meaning the force of attraction between the positive nucleus and the outer electron shell decreases
- this makes it easier to remove the electron as there’s less force of attraction - this means they are more reactive
what are the elements in group 7 called
the halogens
what do all halogens exist as
all go round in pairs (diatomic molecules - molecules that contain only two atoms bonded to one another by a single covalent bond)
halogen properties
- poor conductors of heat and electricity
- toxic and corrosive
how does the reactivity differ in group 7
as you go down the group the reactivity decreases
what are the products when halogens react with metals
metal halide (salt)
what are the products when halogens react with hydrogen
hydrogen halide
what happens in a displacement reaction
a more reactive element takes a place of less reactive element in an ionic compound
explain the trend reactivity in group 7 using the electronic configuration
- group 7 atoms gain one electron when they react
- as you go down the group an electron shell is added and the distance between the outermost shell and the nucleus increases
- this means the force of attraction between the positive nucleus and an incoming negative electron decreases, so the ions do not form so easily and the reactivity decreases
when is there a displacement of halogens
if a halogen is added to a solution of a compound containing a less reactive halogen it will react with the compound and form a new one
redox
reduction and oxidisation occur at the same time
when does a redox reaction take place
during a displacement reaction
oxidisation
‘loss of electrons’
reduction
‘gain of electrons’
OILRIG
Oxidation
Is
Loss
Reduction
Is
Gain
what are the elements called in group 0/8
noble gases
properties of elements in group 0
- are colourless
- have very low melting and boiling points
- a poor conductors of heat and electricity
- INHERT (they do not react)
why are noble gases unreactive
because their atoms already have a stable electronic configuration with a complete outer shell
rate of reaction
the speed at which reactants are turned into products
how can we control the rate of reaction
by altering variables
independent variable
a variable that you change
dependant variable
the variable that you are measuring and depends on the independent variable
controlled variable
variables that remain the same
in a reaction graph, what does it mean if the line is steep
the rate of reaction is fast (this is usually at the start of the reaction)
in a reaction graph, what does it mean if the line goes straight
all the reactants have been used up and the reaction finishes
how can you measure the rate of reaction
- collect gas given off
- weigh the reaction
- colour change
equation work out the rate of reaction
quantity of products formed or quantity of reactants formed
time taken time taken
equation to work out the average rate at a certain time
volume / time
how do you work out the actual rate at a particular time
- draw a tangent on the line of the time it asks
- then work out the gradient of the tangent line - change in volume of product
change in time
collision theory
the reactant particles must collide or ‘bump’ together with enough energy to react
—> the more particles they have means the more energy they can transfer during the collision
activation energy
the minimum amount of energy needed for a reaction to occur is called its activation energy
frequency of collisions
how often the particles collide
what factors affect the rate of reaction
- concentration
- temperature
- particle size/surface area
- presence of a catalyst
explain how concentration affects the rate of reaction
increasing the concentration of solutions increases the rate of reaction because they are more reacting particles in the same volumes of collisions occur more often
explain how surface area affects the rate of reaction
increasing the surface area to volume ratio increases the reaction because there is more surface for collisions to occur on and so collisions occur more often
explain how pressure of gas affects the rate of reaction
increasing the pressure gas increases the reaction because the reacting particles are close together so collision are more often
explain how temperature affects the rate of reaction
increasing the temperature increases the rate of reaction because the reaction particles speed up and have more energy; they therefore collide more often, and more particles have enough energy to react when they collide
catalyst
a substance that speeds up a chemical reaction but is not used up in the process
how to catalysts work
they lower the activation energy so more particles have enough energy to react
how can you model the energy changes during a chemical reaction
reaction profile
exothermic reaction
energy is transferred from the stores of energy in chemical bonds to the surroundings
endothermic reaction
energy is transferred from the surroundings to stores of energy in chemical bonds
in a reaction profile, if the reaction is exothermic, which line is drawn higher the reactants or the products
in a reaction profile, if the reaction is endothermic, which line is drawn higher the reactants or the products
what happens to the temperature in an exothermic reaction
temperature increases
what happens to the temperature in an endothermic reaction
temperature decreases
if the energy change is a positive number, what type of reaction is it
endothermic
if the energy change is a negative number, what type of reaction is it
exothermic
two types of exothermic reactions
- neutralisation (reaction between an acid and a base)
- displacement (the reaction between a metal and a compound of a less reactive metal or between a halogen and a compound of a less reactive halogen)
how can you model the activation energy
in a reaction profile by drawing a ‘hump’ between the reactants and the products
BENDMEX
Breaking is
ENDothermic
Making is
EXothermic
what type of reaction is it if energy is transferred to the reactants to BREAK their bonds and why
endothermic because more energy is given out breaking bonds than is needed to make bonds
what type of reaction is it if energy is transferred to the surroundings as bonds form (MAKE) and why
exothermic because more energy is given out making bonds than is needed to break bonds
bond energy calculation meaning
the total amount of energy in that bond
how to work out the energy change
1) work out the total energy of the bonds in the reactants (bonds broken) - you are given the energy each bond produces, you just have to add and times them accordingly)
2) work out the total energy of the bonds in the products (bonds made) - you are given how much energy each bond produces, you just have to add and times them accordingly)
3) then you do (bonds broken) - (bonds made) = total energy change
—> breaking - making (BendMex)
