Lesson 9, Topic 1
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# Chemical Equation & Chemical Combination (Chemical Bonding)

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Chemical reactions can be represented by chemical equation. The reactants are written at the left hand side (L.H.S) of the equation while the products on the Right hand side (R.H.S).

$$\scriptsize \underset{L.H.S}{REACTANTS} \; \rightarrow \; \underset{R.H.S}{PRODUCTS}$$

### Balancing Chemical Equation

Equations must be balanced in order to agree with the law of conservation of mass which states that in an ordinary chemical reaction, matter can neither be created nor destroyed.

An unbalanced equation would imply that atoms have been created or destroyed. For example, when hydrogen reacts with oxygen to form water, the chemist writes the equation for the reaction as:

$$\scriptsize \underset{H_2}{Hydrogen} \: + \: \underset{O_2}{Oxygen} \: \rightarrow \: \underset{H_2O}{Water}$$ (not balanced)

On the left hand side, there are two atoms of Hydrogen and Oxygen respectively. But on the right-hand side, there are two atoms of Hydrogen and one atom of Oxygen.

To balance the equation, we write two in front of hydrogen on the L.H.S and two in front of water on the R.H.S

$$\scriptsize 2H_{2(g)} \: + \: O_{2(g)} \: \rightarrow \: 2H_2O$$ (balanced)

Rules for Balancing Chemical Equations:

1. Equations must be balanced through the use of co-efficient

2. Common gases like H2, O2, N2, Cl2, etc are diatomic

3. Other elements in their free states e.g K, Na, Cu, Fe, etc are represented by their atomic symbol.

4. Radicals remain unchanged on the left-hand side (LHS) or right-hand side (RHS) of the equation e.g NO3, SO42-, CO32-.

Example I

To balance the equation for the reaction involving magnesium and hydrogen chloride molecules to produce magnesium chloride and hydrogen gas.

$$\scriptsize Mg{(s)} \: + \: HCl_{(aq)} \: \rightarrow \: MgCl_2 + H_2$$

To balance the above equation, H and Cl are 1, 1 on the LHS and 2, 2 on the RHS. We have to write two in front of HCl on the LHS.

$$\scriptsize Mg{(s)} \: + \: 2HCl_{(aq)} \: \rightarrow \: MgCl_2 \: +\: H_2$$

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