GCSE Chemistry - Stoichiometry - Chemical Equations

Objective: Deduce the symbol equation with state symbols for a chemical reaction, given relevant information

Understanding Chemical Equations

A chemical equation is a symbolic representation of a chemical reaction. It uses chemical formulas to show the reactants (starting materials) and products (substances formed). The equation must be balanced, meaning the number of atoms of each element is the same on both sides of the equation, following the law of conservation of mass.

State Symbols

State symbols are abbreviations used to indicate the physical state of substances in a chemical equation:

• (s): Solid
• (l): Liquid
• (g): Gas
• (aq): Aqueous solution (dissolved in water)

Deduceing Balanced Chemical Equations

To deduce a balanced chemical equation, you need to consider the information provided and use your knowledge of balancing equations.

Here's a step-by-step approach:

1. Identify the reactants and products from the given information.
2. Write down the chemical formulas for each reactant and product.
3. Balance the equation by adjusting the coefficients until the number of atoms of each element is the same on both sides.
4. Add state symbols to indicate the physical state of each substance.

Example 1: Reaction of Magnesium with Hydrochloric Acid

Magnesium reacts with hydrochloric acid to produce magnesium chloride and hydrogen gas.

Information given: Magnesium metal reacts with hydrochloric acid to form magnesium chloride solution and hydrogen gas.

Step 1: Identify reactants and products:

• Reactant: Magnesium (Mg)
• Reactant: Hydrochloric acid (HCl)
• Product: Magnesium chloride solution (MgCl₂(aq))
• Product: Hydrogen gas (H₂(g))

Step 2: Write chemical formulas:

• Mg(s)
• HCl(aq)
• MgCl₂(aq)
• H₂(g)

Step 3: Balance the equation:

The balanced equation is: $$Mg(s) + 2HCl(aq) \rightarrow MgCl_2(aq) + H_2(g)$$

Step 4: Add state symbols:

The balanced chemical equation with state symbols is: $$Mg(s) + 2HCl(aq) \rightarrow MgCl_2(aq) + H_2(g)$$

Example 2: Combustion of Methane

Methane (CH₄) undergoes combustion in the presence of oxygen to produce carbon dioxide and water.

Information given: Methane gas burns in air to produce carbon dioxide and water.

Step 1: Identify reactants and products:

• Reactant: Methane gas (CH₄(g))
• Reactant: Oxygen (O₂(g))
• Product: Carbon dioxide (CO₂(g))
• Product: Water (H₂O(g))

Step 2: Write chemical formulas:

• CH₄(g)
• O₂(g)
• CO₂(g)
• H₂O(g)

Step 3: Balance the equation:

The balanced equation is: $$CH_4(g) + 2O_2(g) \rightarrow CO_2(g) + 2H_2O(g)$$

Step 4: Add state symbols:

The balanced chemical equation with state symbols is: $$CH_4(g) + 2O_2(g) \rightarrow CO_2(g) + 2H_2O(g)$$

Practice

Question 1: Iron(III) oxide reacts with hydrochloric acid to produce iron(II) chloride solution and water. Deduce the balanced symbol equation with state symbols.

Answer: $$Fe_2O_3(s) + 6HCl(aq) \rightarrow 2FeCl_3(aq) + 3H_2O(l)$$

Reactants	Products
Magnesium (Mg)	Magnesium chloride solution (MgCl2(aq))
Hydrochloric acid (HCl)	Hydrogen gas (H2(g))