Year 10 EOY exams w/yr9 stuff CHEM

ENDO

takes energy temps drop

EXO

give energy temp rises

Example of ENDO

melting any solid

cooking

Dissolving salt in water

Example of EXO

explosions

combustion reaction

respiration

Law of conservation of mass

Energy cannot be created or destroyed only transformed or transfered from one form to another

If a reactant transfers energy TO the surroundings

reactants>products

difference in energy = energy transfered

If a reactant transfers energy FROM the surroundings

products>reactants

Difference in energy = energy transfered

Why is a reaction EXO

Because there is more energy released in bond making than bond breaking

Why is a reaction ENDO

because more energy is absorbed in bond breaking than is released in bond making

When bonds break it is

ENDOthermic

When bonds are made it is

EXOthermic

-kJ/mol

EXO

+kJ/mol

ENDO

Average rate 1

quantity of reactants used/time taken for change

Average rate 2

Quantity of products formed/ time taken for change

How do reactions happen

2 particles must colide with enough energy and the correct orientation

Activation energy Ea

it is the minimum amount of energy required for a reaction to occur

The rate of reaction depends on the

frequency of successful collisions

how to increase successful collision

increase number of collisions, more particles

increase the proportion of the total that are sussesful, more energy

How to change the rate of reaction

Increase or decrease

Temperature

concentration/ pressure

surface area of solid

catalyst

How temperature changes rate

Heat up

Ke Up

energy of collision up

more frequent successful collisions

rate up

How pressure of concentration changes rate

pressure/concentration up

more particle in given volume

total frequency up

rate up

How surface area changes rate

surface area up, Number of reactants up, total frequency of collisions up, Successful collisions up, rate up

Catalyst

it is a substance that speeds up a reaction but doesn’t get used in the reaction

how do catalysts speed up reactions

they provide an alternate reaction pathway with lower activation energy

Concentration

mass g/ volume dm³

Temperature change neutralisation

put dilute hydrochloric acid into polystyrene cup

measure temp of acid

add sodium hydroxide

put lid on with thermometer in it

read temperature when thermometer stops changing

Temperature change neutralisation

more sodium hydroxide =

Higher temp

Reactivity of metals practical

place same amount of zinc iron magnesium into separate beakers

put same amount of acid into each beaker and measure tempature

higher the temp change higher the reactivity of the metal

rates of reaction disappearing cross

put sodium thiosulfate in a conical flask on top of a printed cross, add water, add hydrochloric acid, measure how much time it takes for the cross to disappear, Repeat with increasing amounts of sodium thiosulfate and decreasing amount of water.

rates of reaction disappearing cross

conclusion

higher concentration = less time for cross to disappear.

suface area : ratio

Divide the surface area by the volume.

Uncertainty

half the range

Endothermic

Takes energy, temp drops

What is the relative charge of a proton

+1

What is the relative charge of an electron

-1

What is the relative charge of a neutron

0

What is the relative mass of a proton

1

What is the relative mass of a neutron

1

What is the relative mass of an electron

almost 0 or very small

Number of neutrons

mass number-proton number

atomic mass

number of protons + electrons

What are isotopes?

they are atoms with the same number of protons but a different number of neutrons

relative atomic mass (for isotopes)

( mass X % of element)+ (mass X % of element) / 100

What is ionic bonding?

it is the electrostatic force of atraction between oppositly charged ions.

Metals always

lose electrons and form positive ions.

Non-metals

gain electrons and form negitive ions

What is covalent bonding

it is the electrostatic force of attraction between shared electrons

what is giant covelant bonding?

it is when millions of atoms are joined together by covelant bonding. this produces giant covelant stuctures not molecules

In diamond all carbon atoms are bonded to

4 other atoms

In graphite every carbon atom is bonded to

3 others

giant covelant stuctures have

high boiling and melting points. they are hard but brittle

Allotrope

an element that exists in different forms.

graphite is soft because

the layers can be broken down because the weak forces of atraction can be easily broken.

How can graphite conduct electricity?

carbon has 4 electons to bond with. in graphite only 3 are used. the electron can move through the layers and carry charge the extra electron that isn’t used in bonding is called delocalised.

mass

formula mass X moles

Metals have high density

because they are densely packed in a lattice. they have high melting and boiling points because the metalic bonds are very strong and need alot of energy to break the bonds

Alloys are

mixtures of a metal and at leat one other element

Why does alloying make a metal stronger?

Normalyy metals have a regular arrangement. the added element makes the arrangement irregular and then it is harder for the layers to slide over each other.

A metalic bond is the electrostatic force between positivly charged ions and the delocalised electron.

Oxidation is a

loss of electrons

Oxygen gained

reduction

what is an ore

it is the extraction of metals from rocks for a profit

Electrolysis

pass an electric current through the molten compound

displacement

heat the compound with carbon, the carbon displaces the less reactive metal.

Atoms are

made up of a core nucleus which contains protons and neutrons. the nucleus is surrounded by electrons which are in electron shells.

John Dalton

developed a theory that everything is made up of atoms, he developed this theory form a greek philosopher called democritus

JJ Thompson

discovered that electron created the plum pudding model, an atom was a ball of positive charge with electrons evenly distributed in it

Alpha scattering experiment

Ernest ruderford fired alpha particles at gold foil. most of the particles when straight through the gold foil but few were scattered in different directions. rudderford then suggested that the atom was mostly empty space and that there was a concentration of positive charge in the atom.

the nuclear model

the mass of an atom is concentrated at the centre, the nucleus has a positive charge.

Neils Bohr suggested

that electrons orbited the nucleus

Ernest ruderford

discovered the proton

James chadwick

dicovered the neutron

Properties of group 1

they are soft, they have a low density, they have low boiling and melting points, they react with the group 7 elements,

The reactivity in group 1

increases further down the group you go, this is because the distance between the outer electrons. this means the force of atraction holding the outer electron in place becomes much easier to lose making it more reactive.

Group 1 is also called the

alkali metals

Group 7 is called the halogens

Group 7 form

-1 ions because they gain an electron

Group 7

extist in pairs

Group 0 aka

the noble gases

Group 0 are unreactive because

they have a full outer shell

Dimitri mendeleev

created the periodic table

The PT was origanally arraneged

based on atomic weight

What was the problem with arrganging the PT in atomic weight

Hydrogen and helium did not fit into only one group and it caused controversy.

How did Mendeleev organise the PT

by atomic weight and left spaces for undiscovered elements.

Ions are

an atom of a group of them that have an electrical charge

Rf value

Distance travelled by spot/ distance travelled by solvent

Chromatography

is used to seperate mixtures and identify what is in the mixture

GCSE required practical chromatography

Draw pencil line on short edge of chromotography paper, add ink on the line at 0.5 cm gaps, Stand paper in beaker with water in it, make sure water does not go over pencil line water for ink to travel at least 3/4 up the page. remove paper from beaker. measure Rf value and record results in a table.

Law of conservation of mass

mass cannot be created or destroyed during a chemical reaction,

Formula Mass (Mr)

Sum of atomic masses (bigger number) in a chemical compound

Types of bonding

Covalent, Metallic, Ionic

Covalent

Non-metals only, Electron sharing,

Giant covalent bonding 1

When millions of atoms are joined together by covalent bonding.

Giant covalent bonding How strong are the bonds

All of the bonds are very strong. They have high melting and boiling points

Allotopes

an element that exists in different forms

Metallic bonding

A metallic bond is the electrostatic force between positive metal ions and the delocalised electrons.