Chemical Equations

A chemical equation is a balanced account of a chemical transaction. It is not merely a qualitative statement, but it also gives quantitative information of a chemical reaction.

OR

The representation of a chemical reaction in a condensed form using chemical formulae is called as the chemical equation.

• Word equations use names; chemical equations use formulas.
• Reactants → Products, with arrow showing reaction direction.
• Use + between two or more reactants or products.
• Show states: (s), (l), (g), (aq); use ↑ for gas, ↓ for precipitate.
• Heat (Δ) or other conditions go above/below the arrow.

A chemical equation represents a chemical reaction in a concise form using chemical symbols and formulas. It shows the transformation of reactants into products with proper notations.

Word Equation and Chemical Equation:

• A chemical reaction can first be written in words, called a word equation.
  Example:
  Copper sulfate solution + Zinc → Zinc sulfate solution + Copper
• A more condensed representation using chemical formulas is called a chemical equation.
  Example: CuSO₄ + Zn → ZnSO₄ + Cu

Reactants are written on the left and products on the right, separated by an arrow (→) indicating the direction of the reaction.

Multiple reactants or products are separated by a plus sign (+).

Physical states are indicated using symbols:

• Solid: (s), Liquid: (l), Gas: (g), Aqueous solution: (aq).
• A gas product can also be indicated with an upward arrow (↑), and an insoluble solid (precipitate) with a downward arrow (↓).

Example with states: CuSO₄(aq) + Zn(s) → ZnSO₄(aq) + Cu(s)

Heat and Reaction Conditions:

1. When heat is required for a reaction, the symbol Δ (delta) is placed above the arrow.
   Example:
   CaCO₃(s) → ΔCaO(s) + CO₂↑
2. If heat is released during a reaction, it is explicitly written.
   Example:
   CuSO₄(aq) + Zn(s) → ZnSO₄(aq) + Cu(s) + Heat​​
3. Special conditions such as temperature, pressure, or catalysts are mentioned above or below the arrow.
   Example:
   \[\mathrm{Vegetable~oil~(l)+H_2(g)}\quad\frac{60^oC}{\text{Ni Catalyst}}\quad\mathrm{Vanaspathi~ghee~(s)}\] 

Examples of Reactions:

• Reaction with concentrated nitric acid
  Cu(s) + 4HNO₃(aq) → Cu(NO₃)₂(aq) + 2NO₂(g) + 2H₂O(l)
  (Nitrogen dioxide (NO₂) is a reddish poisonous gas.)
• Reaction with dilute nitric acid
  3Cu(s) + 8HNO₃(aq) → 3Cu(NO₃)₂(aq) + 2NO(g) + 4H₂O(l)
  (Nitric oxide (NO) gas is formed instead of NO₂)

1. Aim: To observe the formation of a precipitate in a chemical reaction and verify the law of conservation of mass.

2. Requirements

• Apparatus: test tube, conical flask, balance, thread, rubber cork.
• Chemicals: Sodium chloride solution (NaCl) and silver nitrate solution (AgNO₃).

3. Procedure

1. Take a conical flask and fill it with sodium chloride solution.
2. Fill a test tube with silver nitrate solution and tie a thread to it.
3. Carefully insert the test tube into the conical flask without mixing the solutions and seal the flask with a rubber cork to make it airtight.
4. Weigh the conical flask using a balance and record the mass.
5. Tilt the conical flask to mix the silver nitrate solution with the sodium chloride solution.
6. Observe any visible changes, such as the formation of a precipitate.
7. Weigh the conical flask again and compare it with the initial mass.

\[\begin{array}
{c}\mathrm{AgNO}_3(\mathrm{aq})+\mathrm{NaCl}(\mathrm{aq})\longrightarrow\mathrm{AgCl}\downarrow+\mathrm{NaNO}_3(\mathrm{aq}) \\
\end{array}\]

                                                   (white)

The reaction of sodium chloride with silver nitrate

4. Observation

• A white precipitate of silver chloride (AgCl) forms, indicating a chemical reaction.
• The total mass remains unchanged before and after the reaction.

5. Conclusion: The reaction between silver nitrate and sodium chloride results in the formation of an insoluble white precipitate of silver chloride. However, the total mass remains constant, confirming the law of conservation of mass.