Phases in chemical reactions

Phases in chemical reactions

Lessons

• A fully detailed chemical equation should show the state (or phase) of matter that the chemical atoms are in.

• These states are:
\circ Solid, given the symbol (s)
\circ Liquid, given the symbol (l)
\circ Gas, given the symbol (g)
\circ 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.
• Crystals, powder and precipitate are all solid forms.

• Vapour is particles of a substance becoming the gas phase.

• 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)+_{\;(aq)} + NaOH(aq)_{\;(aq)}

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.
  • 1.
    Building on chemical equations
    a)
    Information in a chemical equation.

    b)
    Chemical phases and how to spot them.

    c)
    Other key phase/state language.


  • 2.
    Discuss
    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


  • 3.
    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 (MgCl2_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 (Na2_2CO3_3) powder react to form sodium chloride in solution, water and bubbles of carbon dioxide.