Rates of Reaction 3
Catalysts can also be described with this distribution. A catalyst is defined as a substance that increases the speed of a reaction without being used up itself. The activation energy has been lowered, so the area that is shaded moves closer to the left of the graph, giving a higher proportion of particles with enough activation energy to react as seen in the diagram to the right. Catalysts can be described as either heterogeneous or homogeneous.  Heterogeneous catalysts are when the catalyst is in a different phase when compared to the reactants. An example is the catalytic converter in cars. Solid Platinum metal is used and combines with the gases that are given off. Homogeneous are the opposite, the same phase is used for both catalyst and reactants. An example of this is Esterification when making solvents.

Rates of Reaction 3

Catalysts can also be described with this distribution. A catalyst is defined as a substance that increases the speed of a reaction without being used up itself. The activation energy has been lowered, so the area that is shaded moves closer to the left of the graph, giving a higher proportion of particles with enough activation energy to react as seen in the diagram to the right. Catalysts can be described as either heterogeneous or homogeneous.  Heterogeneous catalysts are when the catalyst is in a different phase when compared to the reactants. An example is the catalytic converter in cars. Solid Platinum metal is used and combines with the gases that are given off. Homogeneous are the opposite, the same phase is used for both catalyst and reactants. An example of this is Esterification when making solvents.

Rates of Reaction 2


The increase of temperature can be illustrated by the Maxwell-Boltzmann distribution. The curve labelled T1 on the diagram to the left shows a lower temperature than T2. It is the area underneath the curve that we are interested in and not the actual curve itself. Behind the line marked activation energy in the shaded area represents the actual amount of particles with enough energy to react. As we increase the temperature of the reactants, the curve flattens and its peak moves to the right. The shaded area increases as the number of particles with enough activation energy to react increases also.

Rates of Reaction 2

The increase of temperature can be illustrated by the Maxwell-Boltzmann distribution. The curve labelled T1 on the diagram to the left shows a lower temperature than T2. It is the area underneath the curve that we are interested in and not the actual curve itself. Behind the line marked activation energy in the shaded area represents the actual amount of particles with enough energy to react. As we increase the temperature of the reactants, the curve flattens and its peak moves to the right. The shaded area increases as the number of particles with enough activation energy to react increases also.

Rates Of Reaction 1

The factors that effect the rates of reactions are temperature, concentration, surface area and catalysts. To understand how they work to increase the rate of reaction, firstly we need to consider the collision theory. The collision theory states that in order for particles to react with each other they must collide. For this collision to take place two things are needed; enough activation energy and the orientation of the molecule to be correct. Most of the collisions that occur do not meet the criteria however, so will not react. Activation energy is the minimum energy required for particles to react.

Increasing the temperature of the reactants gives the particles more energy, causing them to speed up. The more the particles are moving, the more they are likely to collide.

Increasing the concentration of one or more of the reactants in the same volume means there is a much higher chance of the particle colliding. However, as the reactants are used up the concentration falls so the rate will begin to slow down as the reaction continues.

As the surface area increases there are more particles readily available to react, meaning there are more collisions. Using a powder instead of a granule means that the reaction will occur quicker.

Finally, using a catalyst will lower the activation energy of the reactants so that more of the particles will be able to react.

Have opened the A Level biology revision blog at the link below

A level biology

Electron Pair Repulsion Theory

  • Electron pair repulsion theory assumes that atoms in a molecule will be arranged in a way that the repulsion of the electron pairs surrounding it will be minimised.
  • This theory allows us to predict the shapes of molecules.

Greatest repulsion

lone pair - lone pair
lone pair - bond pair
bond pair - bond pair

Least repulsion

Electronegativity

  • Electronegativity is the ability of an atom to draw electrons towards itself.
  • In covalent bonds, if the atoms are the same, their electronegativity is the electrons are shared equally.
  • If the atoms are different, one of the atoms will have more pull on the electrons than the other.
  • This leads to bond polarity.
  • Electronegativity is measured on the Pauling scale.
  • The scale runs for 0-4, 0 having the least pull and 4 having the highest pull. The most electronegative element in Fluorine.

Fundamental particles & Sub shell Theory

An atom is the basis of matter. It is made up of three distinct parts; the protons, neutrons and electrons. The diagram below shows a diagram of a carbon atom that you should all be familiar with.

The protons and neutrons are concentrated in the nucleus at the center of the atom. This gives the nucleus a positive charge. The electrons spinning around the outside have negative charge. The negative charges and the positive charge match up in order to make the atom stable.

  • The relative charge of a proton is +1.
  • The relative charge of an electron is -1.
  • The relative charge of a neutron is 0.

The relative masses of protons and neutrons is 1. The relative mass of an electron is 0.0005. An electron is considerably smaller than a proton or neutron, but is the electron which allows bonding to other atoms to take place.

From GSCE Chemistry, you may remember that electrons fill up shells. The first shell takes 2 electrons and the next can take 8 electrons. If the outer shell isn’t full, an atom can bind with another atom in order to make itself stable. We are going to expand on that theory.

The shells are split into smaller parts known as sub shells. The sub shells are known as S, P, D & F. Within these sub shells are orbitals. Orbitals are small clouds where there is a 95% chance of finding an electron. In each sub shell there are a certain number of orbitals and can contain a certain amount of electrons.

  • S can 2 electrons and 1 Orbital.
  • P has 6 electrons and 3 Orbitals.
  • D has 10 electrons and 5 Orbitals.
  • F has 14 electrons and 7 Orbitals.

The rules from GCSE still apply. The first shell can only contain 2 electrons so only has a S orbital. Taking Helium for instance, see the diagram below, it’s electronic configuration would be written as 1S2. 1 is the main energy level as it is in the first shell, s is the letter of the sub shell and 2 is the number of electrons.

Lithium’s configuration would be 1s2, 2s1. It has it’s first shell fun and it’s second shell has one electron in. After the 2s sub shell is full, we only have 2 electrons in the shell as a whole, so we need to fill the rest of the shell before moving on to the the third shell. This is where we fill up the P sub shell. Carbon’s configuration would therefore be 1s2, 2s2, 2p2. And we can go on until we reach higher configurations like Silicon’s 1s2 2s2 2p6 3s2 3p4.

So, this is a new project of mine.

I’ve been thinking about tutoring for a while, but I started thinking recently about hitting a larger audience. A lot of my lecturers at university have started using Twitter as a means to send us relevant information for our cases, i.e. scientific papers in journals and useful revision tools. I thought, why couldn’t I do the same for A level or BTEC students?

I am currently studying in the second year of a degree in Biochemistry so I have a vast knowledge of both biology and chemistry. I plan to set up a biology blog similar to this one.

I am aiming to follow the AQA specification as this is the one I am most familiar with, however this does not mean that the revision resources that I am providing cannot be used for other specifications or for other qualifications entirely.

I hope you enjoy and hope you find these resources useful. Feedback would be great. Thanks.