National 5 Chemistry

Rates Of Reaction:

Chemical reactions can be very quick, or very slow, such as an explosion or the corrosion of iron. Several factors that affect the rate of reaction are:


Temperature – The higher the temperature, the faster the reaction.

The lower the temperature, the slower the reaction.


Concentration – The higher the concentration, the faster the reaction.

The lower the concentration, the slower the reaction.


Particle size – The smaller the particle size, the faster the reaction.

The larger the particle size, the slower the reaction.


Catalysts – Catalysts alter the rate of reaction but are not used up IN the reaction. (Unless it is poisoned)

Most catalysts affect the rate of reaction.

What are catalysts, and what do they do?

Catalysts are used as they allow reactions to be performed at a lower temperture, which saved energy and money. They also increase the rate of reaction.


There are two types of catalysts:

Homogenous catalyst – is in the same state as the reactants, these are available in all states.

Heterogeneous catalyst – is in a different state from the reactants, and are usually only available in the solid state.

Following the course of a reaction:

There are two common ways of monitoring a reaction. These are measuring the volume of ghas produced and measuring the loss in mass over a period of time. These measurments are used to produce rate graphs which tell many things about the reaction.


The units for the rate are: The volume is given in cm3  whilst the time is given in seconds, so the rate is cm31.


Rate graphs can be used to calculate the rate of the reaction using the following equation:


Rate = Change in volume 

Change in time

The Atom:

Atoms are made up of three smaller particles:


Electrons – Negatively charged particles that spin around the positive centre of the atom in circles, called energy levels. Their mass is so small it is nearly zero.


Protons – Positively charged particles that are contained in the nucleus of the atom, they have a relative mass of 1.


Neutrons – Neutrons are also contained in the nucleus of the atom but have no charge. Theyhave a relative mass of 1.


Elements are arranged in the periodic table in order of increasing atomic number. For example, hydrogen has the atomic number of 1, helium 2 and lithum 3 and so on. The atomic number gives the number of protons in the atom, from this, the number of electrons can be worked out.


The electrons that surround the nuclei are contained in energy levels, these energy levels can only hold a certain amount of electrons. The first energy level (the one nearest the nucleus) can hold a maximum of two electrons. The other energy levels can hold 8 electrons (this is only true for the first twenty elements.)


To work out how many neutrons are in the nucleus of an atom, you need the mass number of the atom. The mass number is given in the top left of the element’s symbol. To find out the number of neutrons, the number of protons needs to be deducted from the mass number. Electrons have a mass of 0 and do not effect the mass of an atom.


The mass of an element is equal to the number of protons + the number of neutrons.


The masses of the atoms of an element are not always the same, they can have different weights. 


For example, 612C and 613C are both carbon atoms.


They are isotopes; they have the same number of protons but different number of neutrons.


Isotopes are atoms with the same atomic number but different mass numbers.


Atoms are neutral becauise they have an equal number of positive protons and negative electrons, but when the number of positive protons and negative electrons in a particle are not equal, an ion is formed.


An ion is a charged particle and they are gained when an atom gains or loses electrons.


Metal atoms lose electrons to form positive ions and non-metal atoms gain electrons to form negative ions.

Ions 2:
The reason that atoms gain or lose electrons is because of noble gases. All elements in the periodic table want to be like them as they have a stable electron arrangement.


A molecules is two or more atoms joined together by covalent bonding. A molecule is usually made up of non-metal atoms only.


Water (H2O) is an example of a molecule. It has two hydrogen atoms and one oxygen atom held together by bonds.

Covalent Bonds:

All elements in the periodic table want to be like noble gases, and have a full outer energy level. For example, neon has eight outer electrons whereas oxygen only has six outer electrons so to become stable like a noble gas, it must gain two electrons. Hydrogen has only on outer electron and will gain one more to achieve the same arrangement as its nearest noble gas, helium. 


To do this, the element has to form bonds. The bonds formed are called covalent bonds.

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