(a) State the various characteristics of chemical reactions.
(b) state one charactoristie each fo the chemical reaction which takes place when
(i) dilute hydrochloride acid is added to sodium carbonate
(ii) lemon juice is added gradually to potassium permanganate solution
(iii) dilute sulphuric acid is added to barium chloride solution
(iv) quicklime is treated with water
(v) wax is burned in the form of a candle

Answer

### Step-by-Step Text Solution

**(a) Characteristics of Chemical Reactions:**

1. **Evolution of Gas:** Many chemical reactions produce gas as a product, which can be observed as bubbles or effervescence.

2. **Change of Color:** A chemical reaction may result in a noticeable change in color, indicating that new substances are formed.

3. **Formation of Precipitate (PPT):** In some reactions, a solid precipitate forms when two solutions are mixed, indicating a chemical change.

4. **Change in Temperature:** Chemical reactions can either release heat (exothermic) or absorb heat (endothermic), leading to a change in temperature.

5. **Change of State:** A chemical reaction may involve a change in the physical state of the reactants or products (solid, liquid, gas).

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**(b) Characteristics of Specific Chemical Reactions:**

1. **Dilute Hydrochloric Acid and Sodium Carbonate:**
- **Reaction:** \( \text{Na}_2\text{CO}_3 + 2\text{HCl} \rightarrow 2\text{NaCl} + \text{H}_2\text{O} + \text{CO}_2 \)
- **Characteristic:** Evolution of gas (carbon dioxide, \( \text{CO}_2 \)).

2. **Lemon Juice and Potassium Permanganate:**
- **Reaction:** \( \text{KMnO}_4 + \text{Lemon Juice} \rightarrow \text{Mn}^{2+} + \text{other products} \)
- **Characteristic:** Change of color (from purple to green).

3. **Dilute Sulfuric Acid and Barium Chloride:**
- **Reaction:** \( \text{H}_2\text{SO}_4 + \text{BaCl}_2 \rightarrow \text{BaSO}_4 \downarrow + 2\text{HCl} \)
- **Characteristic:** Formation of precipitate (barium sulfate, \( \text{BaSO}_4 \)).

4. **Quicklime and Water:**
- **Reaction:** \( \text{CaO} + \text{H}_2\text{O} \rightarrow \text{Ca(OH)}_2 \)
- **Characteristic:** Change of state (solid quicklime to liquid calcium hydroxide).

5. **Burning of Wax in a Candle:**
- **Reaction:** \( \text{C}_{n}\text{H}_{2n+2} + O_2 \rightarrow CO_2 + H_2O + \text{heat} \)
- **Characteristic:** Change in temperature (heat is released during combustion).

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