Skip to content
MathsGenie logo
Open app

Course home

  1. GCSE
  3. Chemistry AQA
  5. Revision guides

2.2.2 State symbols

2.2.2 State symbols in chemical equations

State symbols: each formula shows the physical state of the substance

Definition

State symbol

A symbol in a chemical equation that shows whether a substance is solid, liquid, gas or dissolved in water.

  1. A state symbol is a lower-case letter in brackets that shows the physical state of a substance in a chemical equation.
  2. State symbols let you tell apart solids, liquids, gases and substances dissolved in water.
  3. The correct state symbol depends on the substance and the conditions under which the reaction takes place.
Key Idea
  • Write a state symbol immediately after the formula of each substance.
  • State symbols give information about a substance but are not part of its chemical formula.

The four symbols distinguish the three states of matter from aqueous solutions

Definition

Aqueous solution

A mixture formed when a substance is dissolved in water.

  1. Solid, (s)(\text{s})(s)
    1. Use (s)(\text{s})(s) when the substance is a solid under the reaction conditions.
  2. Liquid, (l)(\text{l})(l)
    1. Use (l)(\text{l})(l) when the substance is a pure liquid.
  3. Gas, (g)(\text{g})(g)
    1. Use (g)(\text{g})(g) when the substance is a gas under the reaction conditions.
  4. Aqueous, (aq)(\text{aq})(aq)
    1. Use (aq)(\text{aq})(aq) when the substance is dissolved in water to form an aqueous solution.
Common Mistake
  • Do not use (l)(\text{l})(l) for a substance just because it is present in a solution.
  • A pure liquid takes (l)(\text{l})(l), while a substance dissolved in water takes (aq)(\text{aq})(aq).

State symbols follow formulae, while coefficients stay at the front

Definition

Coefficient

A large whole number placed before a chemical formula to show the relative number of particles or moles in a balanced equation.

  1. Write each state symbol immediately after the formula it describes, such as O2(g)\text{O}_2(\text{g})O2​(g) or MgO(s)\text{MgO}(\text{s})MgO(s).
  2. Write a coefficient before a formula when balancing an equation, such as 2Mg(s)2\text{Mg}(\text{s})2Mg(s).
  3. Include a state symbol for every reactant and product when a question asks for them.
  4. Keep the chemical formula unchanged when you add a state symbol.
Example
  • Burning magnesium uses solid magnesium and oxygen gas to make solid magnesium oxide.
    • 2Mg(s)+O2(g)→2MgO(s)2\text{Mg}(\text{s}) + \text{O}_2(\text{g}) \rightarrow 2\text{MgO}(\text{s})2Mg(s)+O2​(g)→2MgO(s)
  • Neutralisation can involve two aqueous solutions making an aqueous salt and liquid water.
    • HCl(aq)+NaOH(aq)→NaCl(aq)+H2O(l)\text{HCl}(\text{aq}) + \text{NaOH}(\text{aq}) \rightarrow \text{NaCl}(\text{aq}) + \text{H}_2\text{O}(\text{l})HCl(aq)+NaOH(aq)→NaCl(aq)+H2​O(l)

Reaction conditions determine which state symbol is correct

  1. Use the information in the question to decide the physical state of each substance during the reaction.
  2. The same substance can have different state symbols under different conditions.
  3. Water at room temperature is written as H2O(l)\text{H}_2\text{O}(\text{l})H2​O(l), while steam is written as H2O(g)\text{H}_2\text{O}(\text{g})H2​O(g).
  4. Solid sodium chloride is written as NaCl(s)\text{NaCl}(\text{s})NaCl(s), while sodium chloride dissolved in water is written as NaCl(aq)\text{NaCl}(\text{aq})NaCl(aq).
  5. Do not assume every substance containing water is aqueous, because (aq)(\text{aq})(aq) means dissolved in water rather than mixed with water.
Note
  • A question may give the states directly through words such as solid, molten, gas or solution.
  • If a substance is described as molten, it is a liquid and takes the symbol (l)(\text{l})(l).

A complete equation gives the correct state for every reactant and product

Definition

Reactant

A reactant is a substance that is changed or used up during a chemical reaction.

  1. Check that every formula has a state symbol when the question asks you to include them.
  2. Check that (aq)(\text{aq})(aq) is used only for a substance dissolved in water.
  3. Check that each symbol is lower case and enclosed in round brackets.
  4. Check that coefficients come before formulae and state symbols come after them.
  5. Check that the state symbols match the conditions described in the question.
Self review
  • Which state symbol shows that a substance is a solid?
  • What does the state symbol (aq)(\text{aq})(aq) mean?
  • Where should a state symbol be placed in relation to a chemical formula?
  • What is the difference between H2O(l)\text{H}_2\text{O}(\text{l})H2​O(l) and H2O(g)\text{H}_2\text{O}(\text{g})H2​O(g)?
  • Which state symbol should be used for molten sodium chloride?
PreviousNext

How was this guide?

Teach Genie

Review 2.2.2 State symbols by teaching Genie

Teach it back in your own words, spot gaps, and remember it better.

Start teaching
Genie and Baby Genie

Lesson

Recap your knowledge with an interactive lesson

7 minute activity

Start lesson

Chemical equation showing the positions of coefficients and state symbols, with a legend for solid, liquid, gas and aqueous symbols

A state symbol is a lower-case letter in round brackets that shows the physical state of a substance in a chemical equation. It distinguishes a solid, pure liquid, gas or substance dissolved in water.

The four state symbols are (s)(\text{s})(s) for solid, (l)(\text{l})(l) for pure liquid, (g)(\text{g})(g) for gas and (aq)(\text{aq})(aq) for dissolved in water. Write the state symbol immediately after the formula it describes.

Flashcards

Remember key concepts with flashcards

23 flashcards

Practice flashcards

What information does a state symbol give in a chemical equation?

2.2.2 State symbols Revision Guide

  1. GCSE
  2. /Chemistry
  3. /2.2.2 State symbols

Revision notes for AQA GCSE Chemistry 2.2.2 State symbols. Open the guide for explanations and worked examples. Written against the AQA GCSE Chemistry (8462) specification, so the content matches what's examinable rather than general Chemistry background.

Revision guides