Question

How is a chemical equation written? How can a chemical equation be made more informative?

Answer 1

Chemical equations for chemical reactions are written as follows:

Step-1: Forming a skeletal equation

1. Determine the reactants and products of the chemical reaction.
2. Put the formulae or symbols of the reactants on the left-hand side with a plus sign (+) between them.
3. Put the formulae or symbols of the products on the right-hand side with a plus sign (+) between them.
4. The reactants and products are separated by an arrow(⇢)

$\mathrm{HCl}\left(\mathrm{l}\right)+\mathrm{NaOH}\left(\mathrm{aq}\right)\to \mathrm{NaCl}\left(\mathrm{s}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{aq}\right)$

Such an equation is called a Skeletal equation.

Step-2: Balancing the equation

1. Count the number of atoms of each element on both sides and if unequal then balance the equation by adjusting the coefficients.

Step-3: Adding more information to the equation:

A chemical reaction can be made more informative by adding the following information to the chemical equation.

1. Reaction condition: The information regarding temperature, pressure, catalysts, etc is provided above the arrow separating reactants and products.

$\mathrm{Reactants}\underset{\mathrm{catalyst}}{\overset{\mathrm{t}°\mathrm{C},\mathrm{p}\mathrm{atm}}{\to }}\mathrm{Products}$

2. Physical states: The physical states of reactants and products can be described using letters such as s,l,g, aq for solid, liquid, gas, and aqueous respectively.

$2\mathrm{Na}\left(\mathrm{s}\right)+2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\to 2\mathrm{NaOH}\left(\mathrm{aq}\right)+{\mathrm{H}}_2\left(\mathrm{g}\right)$

3. Heat absorbed or evolved:

The term exothermic reaction(+Heat) refers to a chemical reaction that produces heat along with its products.

$\mathrm{C}\left(\mathrm{s}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)\to {\mathrm{CO}}_2\left(\mathrm{g}\right)+\mathrm{Heat}(=393\mathrm{kJ}{\mathrm{mol}}^{-1})$

An endothermic reaction(-Heat) absorbs a large amount of heat.

$\mathrm{C}\left(\mathrm{s}\right)+2\mathrm{S}\left(\mathrm{g}\right)\to {\mathrm{CS}}_2\left(\mathrm{g}\right)-\mathrm{Heat}(=92\mathrm{kJ}{\mathrm{mol}}^{-1})$

4. Concentration: This information is added to the chemical equation by adding the word dil. (for dilute) and conc. (for concentrated)

$\mathrm{Zn}\left(\mathrm{s}\right)+\mathrm{dil}.{\mathrm{H}}_2{\mathrm{SO}}_4\left(\mathrm{aq}\right)\to {\mathrm{ZnSO}}_4\left(\mathrm{aq}\right)+{\mathrm{H}}_2\left(\mathrm{g}\right)$

5. Rate of reaction: The rate of reaction describes the speed at which a chemical reaction takes place.

The term ‘fast or ’slow' is added over the arrow depending upon the reaction rate.

$\mathrm{HCl}\left(\mathrm{aq}\right)+\mathrm{NaOH}\left(\mathrm{aq}\right)\stackrel{\mathrm{Fast}}{\to }\mathrm{NaCl}\left(\mathrm{aq}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)$