# Phases in chemical reactions

### Phases in chemical reactions

#### Lessons

In this lesson, we will learn:
• The four phases that describe chemicals in reaction equations.
• Other key descriptive terms for chemicals in reactions.
• Practical reasons why state symbols are included in a chemical equation.

Notes:
• A fully detailed chemical equation should show the state (or phase) of matter that the chemical atoms are in. This is meant to tell you the arrangement of the atoms of the reactants when they engage in the chemical reaction.

• These states are:
• Solid, given the symbol (s)
• Liquid, given the symbol (l)
• Gas, given the symbol (g)
• Aqueous, meaning dissolved in water, and given the symbol (aq)

• The information is important for chemists moving from planning a reaction to performing the experiment. Knowing the state of the product helps plan how you can collect the products of the reaction being done.
• For example, a desired product dissolved in solution would need to be evaporated, and a solid product would need to be filtered to help isolate it.

• There are some common chemical 'forms' of some states - crystals, powder and precipitate are all solid forms.
• Vapour is particles of a substance becoming a gas.

• A solution of a chemical would be described as aqueous. For example "a solution of HCl was reacted with a solution of NaOH" in an equation would be shown as "HCl$_{\;(aq)} +$NaOH$_{\;(aq)}$"
• Introduction
Building on chemical equations
a)
Information in a chemical equation.

b)
Chemical phases and how to spot them.

c)
Other key phase/state language.

• 1.
Recall the different states of matter from descriptions of chemicals.
Write "solid", "liquid", "gas", or "aqueous", next to each term below to show which state it is describing.
a)
Powder

b)
Solution

c)
Vapour

d)
Crystals

e)
Gaseous

f)
Precipitate

• 2.
Write full chemical equations using information from descriptions of laboratory experiments.
Read the following experiment notes and write a balanced chemical equation, with state symbols, to describe what is happening.
a)
Strips of magnesium were weighed out and placed in a beaker. Shortly afterwards, a solution of hydrochloric acid was added to the beaker to produce magnesium chloride (MgCl$_2$) and gaseous hydrogen.

b)
In a reaction vessel, chlorine gas reacts with chunks of sodium metal to form sodium chloride in a reaction releasing a lot of heat energy.

c)
When hot steam is passed over iron filings, gaseous hydrogen and solid iron oxide is produced.

d)
Aqueous hydrochloric acid and sodium carbonate (Na$_2$CO$_3$) powder react to form sodium chloride in solution, water and bubbles of carbon dioxide.