- Burning of coal
- melting of ice
From the above example we can see not all the changes are chemical reactions. In order to find whether a change is a chemical change or not we can use several indicators.
Evidences for chemical reactions:
- Evolving a gas
- a colour change
- change in the temperature
- a precipitate formed
- a sound produced etc.
Word equation for a chemical reaction
These chemical reactions can be represented in a word equation by writing the chemical names of the reactants in the left side, writing the chemical names of the products in the right hand side, connecting them with an arrow.
e.g: Carbon monoxide + oxygen ----> Carbon dioxide
Chemical equations
More information about an equation such as reacting molar ratios and states of the reactants/products can be obtained from a chemical equation. In a chemical equation the correct formula of the reactants and products are written connected with a suitable symbolic arrow. Remember when the formulae are written it should be the natural and stable state of the species. eg: Oxygen O2 , Magnesium Mg, Nitrogen N2
Then the state of the each species should be stated. State is Whether the substance is a solid, liquid, gas or aqueous during the reaction
The state symbols are as follows
Solid (s)
liquid (l)
gas (g)
aqueous/ dissolved in water (aq)
e.g: O2 (g)
Mg(s)
H2O (l)
NaCl(aq)
As the final step number of each type of atom in the left hand side of the equation should be equal to the number of each type of atoms in the right hand side of the equation.
e.g: 2H2 (g) + O2 (g) -> 2 H2O (l)
Questions:
1. write balanced equations with state symbols for the following reactions
a) burning of methane
b) magnesium with hydrochloric acid
Next about rate of reaction
10:55 PM
chemical reactions
evidence for chemical reactions
writing chemical equation
writing word equation
