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

Conservation of mass

Balancing equations

Empirical formula calculations

Uncertainties in measurements: chemistry

Mass in a chemical reaction

Deducing an empirical formula experimentally

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.

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.

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.

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.

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.

Conservation of mass means the total mass of the starting reactants equals the total mass of the products formed.

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.

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

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

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.

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