Chemical Equations and Their Role in Representing Reactions
Analogy- Consider you are baking a cake.
- The recipe specifies exact amounts of flour, sugar, eggs, and butter to create the perfect dessert.
- If you use too much or too little of any ingredient, the result might not turn out as expected.
In chemistry, a chemical equation serves as this "recipe" for a chemical reaction. It tells you the precise ratios of reactants (ingredients) and products (results) involved.
Representing Chemical Reactions with Equations
Definition
Chemical equation
A chemical equation is a symbolic representation of a chemical reaction. It shows the reactants (starting substances) on the left side, the products (substances formed) on the right, and an arrow indicating the direction of the reaction.
$$C_2H_6 + O_2 \rightarrow CO_2 + H_2O$$
- This equation represents the combustion of ethane ($C_2H_6$) in oxygen ($O_2$) to produce carbon dioxide ($CO_2$) and water ($H_2O$).
- However, this equation is not yet complete: it must be balanced to adhere to the law of conservation of mass, which states that matter cannot be created or destroyed in a chemical reaction.
Balancing Chemical Equations: Why and How?
- When balancing a chemical equation, the goal is to ensure the number of atoms of each element is the same on both sides of the equation.
- This reflects the fact that atoms are simply rearranged during a reaction, not created or destroyed.
Steps to Balance a Chemical Equation:
- Write the unbalanced equation:
- Start by listing the reactants and products.
- For example, $C_2H_6 + O_2 \rightarrow CO_2 + H_2O$
- Count the atoms of each element on both sides of the equation.
- Reactants: 2 carbons, 6 hydrogens, 2 oxygens.
- Products: 1 carbon, 2 hydrogens, 3 oxygens.
- Add coefficients to balance the atoms, starting with the element that appears in the fewest compounds.
- Balance carbon: $C_2H_6 + O_2 \rightarrow 2CO_2 + H_2O$.
- Balance hydrogen: $C_2H_6 + O_2 \rightarrow 2CO_2 + 3H_2O$.
- Balance oxygen: $C_2H_6 + 3.5O_2 \rightarrow 2CO_2 + 3H_2O$.
