Introduction to Chemical Equations

Indicators of a Chemical Reaction

• Determining if a Reaction is Occurring: In chemistry, there are five primary signs or indicators that suggest a chemical change is taking place:

  1. Colour change: An alteration in the substance's color.

  2. Production of an odour: The emergence of a scent during the process.

  3. Change in temperature: A shift in the thermal state of the reagents.

  4. Formation of bubbles: This denotes the production of a gas.

  5. Precipitate formed: The appearance of a solid from a liquid-based reaction.

Definition and Dynamics of Chemical Equations

• What is a Chemical Equation?: A chemical equation identifies the specific chemicals involved in a reaction using chemical formulas and symbols.

• The Reaction Process: A reaction involves one or more chemical changes occurring at the same time.

• Rearrangement of Atoms: During a reaction, atoms are rearranged to form new substances. These new substances possess entirely new physical and chemical properties compared to the original substances.

Key Components and Terminology

• Reactants: These are the chemicals present at the beginning of a reaction. They are always positioned on the left side of the arrow.

• Products: These are the chemicals manufactured or formed during the reaction. They are always positioned on the right side of the arrow.

• Equation Symbols:

  • Plus Sign ($+$): Used to separate individual reactants from one another and products from one another.

  • Arrow ($\rightarrow$): Used to separate the reactants (starting chemicals) from the products (resulting chemicals).

• General Representation: $\text{Reactants} \rightarrow \text{Products}$

• Simple Example: $H_2 + O_2 \rightarrow H_2O$

Types of Chemical Equations

• There are three distinct ways to represent a chemical equation:

  1. Word Equation

  2. Skeleton Equation

  3. Balanced Equation (Note: to be discussed further in later lessons).

Word Equations

• Description: Word equations display the reactants and products in full words.

• Limitation: They do not show the physical or chemical makeup (formulas) of the substances involved.

• Example: Hydrogen gas reacts with oxygen gas to form water.

• Practice Exercise:

  • Prompt: Write a word equation for $CaCl_2 + Na_2SO_4 \rightarrow CaSO_4 + NaCl$

  • Translation: Calcium chloride and sodium sulphate react to form calcium sulphate and sodium chloride.

  • Final Word Equation: Calcium chloride + sodium sulphate $\rightarrow$ calcium sulphate + sodium chloride.

Skeleton Equations

• Description: A skeleton equation shows the chemical composition of each substance using its chemical formula.

• Limitation: It does not indicate the specific number of units of reactants that react or the units of product produced (i.e., it does not define "how much").

• Example: $H_2 + O_2 \rightarrow H_2O$

  • In this skeleton equation, notice that the exact amounts of reacting hydrogen and oxygen, and the resulting water, are not quantified.

• Practice Exercise:

  • Prompt: Write a skeleton equation for "Copper (II) oxide reacts with hydrogen sulphate to form copper (II) sulphate and water."

  • Resulting Equation: $CuO + H_2SO_4 \rightarrow CuSO_4 + H_2O$

Notation for States of Matter

• Usage: Symbols are frequently used in chemical equations to display the physical state of matter for each substance.

• Key Symbols:

  • $(aq)$: Aqueous (the substance is dissolved in water).

  • $(s)$: Solid.

  • $(l)$: Liquid.

  • $(g)$: Gas.

• Exemplary Equation with State Symbols: $HCl(aq) + Na(s) \rightarrow NaCl(aq) + H_2(g)$