A chemical equation describes a reaction, indicating the reactants and products.

Oxidation is a type of reaction in which oxygen bonds to elements of the reactants.

Decomposition is a type of reaction in which a reactant compound breaks down into two or more products.

A reaction in which an insoluble salt forms from two solutions is called a precipitation reaction.

Three types of chemical reaction

Chemistry

In the Making salts unit, pupils will learn about the production of pure salts, concentration and strength of acids, and what makes acids acidic and how bases can neutralise them.

In the Understanding Chemical Reactions unit, pupils learned about how atoms rearrange during chemical reactions and the conservation of mass.

This unit covers writing chemical formulae, balancing equations, and using the conservation of mass. It includes calculating moles, empirical formulae, relative formula masses, and theoretical yields. Emphasis is on stoichiometry, concentration, gas volumes, and using standard form.

Calculations involving masses

Conservation of mass means that the combined mass of the starting reactants equals the combined mass of the products formed.

A closed system is one in which matter cannot enter or leave the observed environment, allowing only energy transfer between the system and its surrounding environment.

Reactants are the elements or compounds before a reaction takes place.

Products are the elements or compounds that are formed after a reaction has taken place.

Atoms are the building blocks of all matter.

Conservation of mass

A word equation represents a chemical reaction using the chemical names of the reactants and products.

A chemical formula represents a substance using element symbols and the number / ratio of atoms of each element in the substance.

A symbol equation represents a chemical reaction using the chemical formulas of the reactants and products.

A balanced symbol equation uses coefficients to ensure that the number of atoms of each element is equal on both sides of the equation.

A coefficient is the number placed in front of a chemical formula to balance an equation; it multiplies all the atoms in the formula and shows the ratio of substances in a reaction.

Balancing equations

A mole of something is 6.02 × 10²³ of it. The mass of a mole of a substance is its relative mass expressed in grams.

The relative formula mass (RFM) of a substance is the sum of the relative atomic masses of all the atoms in a formula.

Avogadro's constant is the number of particles in one mole of a substance (6.02 × 10²³ mol⁻¹)

The mole

1 mole of a substance is 6.02 × 10²³ particles of it. The mass of a mole of a substance is its relative mass in grams.

Avogadro's constant is the number of particles in one mole of a substance (6.02 × 10²³ mol⁻¹).

The relative formula mass (RFM or Mᵣ) of a substance is the sum of the relative atomic masses of all the atoms in its formula.

Moles and masses

A substance's empirical formula shows the simplest whole number ratio of atoms of each element in a compound.

The relative formula mass of a substance is the sum of the relative atomic masses of all the atoms in a formula.

A substance's molecular formula shows the actual number of atoms of each element in a molecule of a compound.

Empirical formula calculations: using moles

is the range of measurements within which the true value can be expected to be found. On apparatus, it is half the value of one resolution marking.

provides quantitative information about an object or system.

is an average calculated by adding up the values of a set of measurements and dividing by the number of measurements in the set.

is the smallest change a piece of apparatus can measure - shown by its markings.

a piece of equipment that is designed for a particular use.

Uncertainties in measurements: chemistry

of something is 6.02 × 10²³ of it. The mass of a mole of a substance is its relative mass expressed in grams.

is a piece of equipment that is designed for a particular use.

is the ability to change between units of measurement.

refers to how close a measured value is to the true or standard value.

Representations of a mole

Stoichiometry refers to the molar ratio of the reactants and products in a chemical reaction.

A balanced symbol equation represents a chemical reaction using symbols and coefficients to ensure that the number of atoms of each element is equal on both sides of the equation.

Mass in a chemical reaction: using moles

The reactant that completely reacts, thereby determining the maximum amount of product that can be formed in a chemical reaction. All other reactants will be present in excess.

Any reactant present in a greater amount than is necessary to completely react with the limiting reactant.

The maximum calculated mass of product expected to form from a given amount of reactants.

A mole of a substance contains 6.02 × 10²³ particles of it. The mass of one mole of a substance is its relative mass in grams.

The molar ratio of the reactants to the products in a chemical reaction.

Limiting reactants

To evaluate something is to make a judgement about it with respect to a particular purpose.

Relative atomic mass is the mean mass of an atom relative to 1/12th the mass of an atom of carbon–12.

Deducing an empirical formula experimentally: using moles

Describes a reaction using a symbol equation with coefficients, which ensure there are equal numbers of atoms of each element on both sides of the symbol equation.

Refers to the molar ratio of the reactants and products in a chemical reaction.

Ratio can be used to determine the size of one quantity in relation to another.

Determining an equation from given values

A type of reaction where a reactant compound breaks down into two or more products.

A ratio can be used to determine the size of one quantity in relation to another.

The molar ratio of the reactants and products in a chemical reaction.

A reaction using a symbol equation with coefficients to ensure there are equal numbers of atoms of each element on both sides of the equation.

Determining an equation experimentally: sodium hydrogencarbonate

is how much 3D space matter occupies.  It is usually measured in cm³.

is the volume occupied by one mole of any gas. It is equal to 24 dm³ or 24 000 cm³ at room temperature and pressure.

refers to the molar ratio of the reactants and products in a chemical reaction.

is a property of a substance and is its mass divided by its volume.

Gas volumes

Volume is how much 3D space matter occupies. It is usually measured in cm³.

Molar gas volume is the volume occupied by one mole of any gas. It is equal to 24 dm³ or 24 000 cm³ at room temperature and pressure.

A balanced symbol equation describes a reaction using a symbol equation with coefficients, which ensure there are equal numbers of atoms of each element on both sides of the symbol equation.

Calculations involving masses

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These lessons will be removed by end of Summer Term 2025.