Skip to main content

Writing Equations

Mahi Tuatahi / Do Now 🔗

When finished, get out your device and start working on your experiment document from last period

Ngā Whāinga Ako 🔗

  1. To write word equations to show a chemical reaction
  2. To write symbol equations to show a chemical reactions with symbols of state

Chemical Reactions 🔗

There are two ways we can show a chemical reaction on paper:

  1. Word equations
  2. Symbol equations

Word Equations 🔗

All equations have three parts to them:

  1. Reactants (left-hand side)
  2. Products (right-hand side)
  3. Arrow - means goes to form not equals

$$ \begin{aligned} reactant1 + reactant2 \rightarrow product1 + product2 \end{aligned} $$

Ngohe/Task: Write a word equation for this reaction 🔗

Ella puts 1cm of magnesium strip in 5ml of dilute hydrochloric acid and observes hydrogen gas put off and that the magnesium dissolves into magnesium chloride.

Whakatika / Answer 🔗

Ngohe/Task: Write a word equation for this reaction 🔗

Jake adds 1ml of copper sulfate to 1ml of sodium hydroxide and predicts that copper hydroxide and sodium sulfate will be produced.

Whakatika / Answer 🔗

Symbol Equations 🔗

Symbol equations are very similar, except we use the symbols from the periodic table and we have to give the state of each reactant and product. The state goes in the subscript after the element/compound.

Pātai: Discuss with your partner, what are the four states of matter that we use in chemistry?

SolidLiquidGasAqueous
Subscript(s)(l)(g)(aq)

Ngohe/Task: Write a symbol equation for this reaction 🔗

Ella puts 1cm of magnesium strip in 5ml of dilute hydrochloric acid and observes hydrogen gas put off and that the magnesium dissolves into magnesium chloride.

$$ \begin{aligned} Mg_{(s)} + HCl_{(aq)} \rightarrow H_{2(g)} + MgCl_{(aq)} \end{aligned} $$

Ngohe/Task: Write a word and symbol equation for this reaction 🔗

Jake adds 1ml of copper sulfate to 1ml of sodium hydroxide and predicts that copper hydroxide and sodium sulfate will be produced.

$$ \begin{aligned} CuSO_{4(aq)} + NaOH_{(aq)} \rightarrow Cu(OH){2(s)} + Na{2}SO_{4(s)} \end{aligned} $$

Balancing Equations 🔗

Tauria / Example 🔗

$$ \begin{aligned} Magnesium Metal + Oxygen Gas &\rightarrow Magnesium Oxide \newline Mg_{(s)} + O_{2(g)} &\rightarrow MgO_{(s)} \end{aligned} $$

RHSLHS
Mg
O

It is unbalanced!

RHSLHS
Mg11
O21

Step 1 🔗

Start by balancing the oxygen by putting a two in front of the $MgO$.

$$ \begin{aligned} Mg_{(s)} + O_{2(g)} &\rightarrow 2MgO_{(s)} \end{aligned} $$

| | RHS | LHS | | :-- | :-- | :-- | | Mg | 1 | 2 | | O | 2 | 2 |

Step 2 🔗

Now the magnesium is unbalanced, so we need to put a two in front of the $Mg$.

$$ \begin{aligned} 2Mg_{(s)} + O_{2(g)} &\rightarrow 2MgO_{(s)} \end{aligned} $$

| | RHS | LHS | | :-- | :-- | :-- | | Mg | 2 | 2 | | O | 2 | 2 |

Balanced!

Summary of Symbols 🔗

Mahi / Work 🔗