Lessons 5 + 6 - More balancing and state symbols

3. Balancing a Chemical Equation

Consider the following word equation for a chemical reaction.............

Sodium + chlorine --> sodium chloride

Using all the rules in the above sections, we can turn each of the names into a chemical formula, giving us.....

Na + Cl₂ --> NaCl

There is definitely nothing wrong with any of our chemical formulae here.... the formula of sodium is Na, the formula of chlorine when it is an element is Cl₂ (one of the diatomic elements!) and if we work out the formula of sodium chloride it turns out to be NaCl.

State Symbols

When we have a balanced symbol equation, we often include what are known as 'state symbols' to show what physical state that chemical is in during the reaction. We use the following state symbols in Chemistry.

(s) - solid

(l) - liquid

(g) - gas

(aq) - aqueous solution/dissolved in water

The two people mix up are (l) and (aq). When a substance is (l) it means it is PURE but just in the liquid state. For example, pure water would be H2O(l)

However, when a chemical is dissolved in water, which many are, they are written as (aq). All the acids you are given in the lab are dissolved in water.

Hydrochloric acid is HCl_(aq)

Nitric acid is HNO_3(aq)

Sulfuric acid is H₂SO_4(aq)

Phosphoric acid is H₃PO_{4 (aq)}

A really good way to show the difference between the different state symbols is looking at the following example.......

Imagine taking some glucose, which is a type of sugar and is a white powder It has the chemical formulae of C₆H₁₂O₆

When the glucose exists at room temperature it exists as a solid, so we would write C₆H₁₂O_{6 (s)}

However, we could put glucose into a pan and heat it enough for it to melt. Then we would have turned the glucose into a liquid, which would be C₆H₁₂O_{6 (l)}

But we could have also taken our solid glucose and spooned it into a cup of water. You know that sugar dissolves well in water, so afterwards we would not be able to see the sugar (as it has dissolved and made a solution) but it is still there. We have now got a mixture of glucose dissolved in water, which would be C₆H₁₂O_{6 (aq)}