Class 10 Science Chapter 1: Chemical Reactions and Equations Worksheet (2025 Syllabus)

1. (a) ,
2. (b),
3. (b),
4. (a),
5. (b)
6. (b) $MnO_2$ is reduced to $MnCl_2$ & $HCl$ is oxidized to $Cl$

\[ Mg + 2HCl \rightarrow MgCl_2 + H_2 \]

Yes, a combination reaction can be a redox reaction.

Example:

\[ 2H_2 + O_2 \rightarrow 2H_2O \]

To prevent rusting (corrosion).

• Combination reactions
• Decomposition reactions
• Displacement reactions
• Double displacement reactions
• Oxidation and reduction reactions

A decomposition reaction is one in which a compound breaks down into two or more simpler substances.

\[ 2H_2O \rightarrow 2H_2 + O_2 \]

\[ CuSO_4 + Zn \rightarrow ZnSO_4 + Cu \]

\[ 2Na + 2H_2O \rightarrow 2NaOH + H_2 \]

\[ NaCl + AgNO_3 \rightarrow AgCl \downarrow + NaNO_3 \]

\[ Fe + CuSO_4 \rightarrow FeSO_4 + Cu \]

\[ 6CO_2 + 6H_2O + \text{Sunlight} \rightarrow C_6H_{12}O_6 + 6O_2 \]

\[ 2KClO_3 \rightarrow 2KCl + 3O_2 \]

(i) Reaction of barium chloride and sodium sulphate:

\[ BaCl_2 + Na_2SO_4 \rightarrow BaSO_4 \downarrow + 2NaCl \]

(ii) Reaction of sodium hydroxide and hydrochloric acid:

\[ NaOH + HCl \rightarrow NaCl + H_2O \]

(a) Splitting of water into hydrogen and oxygen: Decomposition reaction

(b) Burning of hydrogen in air: Combination reaction

(c) Action of iron with copper sulphate solution: Displacement reaction

(d) Action of heat on calcium carbonate: Thermal decomposition reaction

(e) Treating silver nitrate with hydrochloric acid: Double displacement reaction and precipitation reaction

Melting ice is a physical change where only the state changes, and the substance remains water. Burning hydrogen in air is a chemical change where hydrogen reacts with oxygen to form a new substance, water, with different chemical properties.

Copper nitrate crystals undergo thermal decomposition upon heating, likely forming copper oxide, which is a black substance. This involves a change in the chemical composition of copper nitrate.

Chlorine is more reactive than iodine and displaces it from potassium iodide solution. The elemental iodine formed dissolves in chloroform, resulting in a purple color.

Seawater contains chloride ions. Silver ions from silver nitrate react with these chloride ions in a double displacement reaction, forming silver chloride, which is insoluble and precipitates out as a white solid.

Here are the characteristic tests for the following gases:

• CO₂ (Carbon Dioxide): When carbon dioxide is passed through lime water (calcium hydroxide), it turns the lime water milky due to the formation of calcium carbonate.
  Reaction: Ca(OH)₂(aq) + CO₂(gas) → CaCO₃(s) + H₂O(l)


• SO₂ (Sulphur Dioxide): Sulphur dioxide can be tested by passing the gas through a solution of acidified potassium dichromate(VI). The orange solution gets decolorized as sulphur dioxide reduces orange potassium dichromate(VI) to green chromium(III) ions. This is a redox reaction.
  Reaction: K₂Cr₂O₇(aq) + H₂SO₄ + 3SO₂ → K₂SO₄ + Cr₂(SO₄)₃ + H₂O


• O₂ (Oxygen): A common test for oxygen is the glowing splint test. In this test, a glowing splint is inserted into a test tube containing the gas. If the splint rekindles and starts to burn brightly, the gas is oxygen.


• H₂ (Hydrogen): A common test for hydrogen is the pop test. In this test, a lit splint is brought near the mouth of the test tube containing the gas. If the gas is hydrogen, it will ignite with a 'pop' sound.

• (a) Zinc metal is added to copper sulphate solution:
  When a piece of zinc metal is added to copper sulphate solution, a displacement reaction occurs. Zinc is more reactive than copper, so it displaces copper from the copper sulphate solution. The blue colour of the copper sulphate solution fades as copper ions are replaced by zinc ions, forming zinc sulphate solution, which is colourless. Copper metal is deposited on the zinc piece as a reddish-brown coating.
  Balanced chemical equation:
  Zn(s) + CuSO₄(aq) → ZnSO₄(aq) + Cu(s)


• (b) Aluminium metal is added to dilute hydrochloric acid:
  When aluminium metal is added to dilute hydrochloric acid, a displacement reaction occurs. Aluminium is more reactive than hydrogen and displaces hydrogen from hydrochloric acid, producing aluminium chloride solution and hydrogen gas. Bubbles of hydrogen gas are observed.
  Balanced chemical equation:
  2Al(s) + 6HCl(aq) → 2AlCl₃(aq) + 3H₂(g)


• (c) Silver metal is added to copper sulphate solution:
  When silver metal is added to copper sulphate solution, no reaction occurs. Silver is less reactive than copper, so it cannot displace copper from its salt solution. Therefore, no observable change is seen in the copper sulphate solution or the silver metal.

A usual chemical equation can be made more informative in the following ways:

(a) Writing Symbols of Physical States: To make a chemical equation more informative, the physical states of the reactants and products are mentioned along with their chemical formulae. The gaseous, liquid, aqueous, and solid states of reactants and products are represented by the notations (g), (l), (aq), and (s), respectively. The word aqueous (aq) is written if the reactant or product is present as a solution in water.

(b) Balancing the Chemical Equation: A chemical equation is balanced so that the numbers of atoms of each type involved in a chemical reaction are the same on the reactant and product sides of the equation. This is in accordance with the law of conservation of mass, which states that mass can neither be created nor destroyed in a chemical reaction.

(c) Including Reaction Conditions: Sometimes the reaction conditions, such as temperature, pressure, catalyst, etc., for the reaction are indicated above and/or below the arrow in the equation. This provides additional information about the conditions under which the reaction occurs. This includes heat given or heat obtained, i.e., whether the reaction is exothermic or endothermic.

A skeletal chemical equation is an unbalanced equation that uses chemical formulas to show the reactants and products of a chemical reaction. It simply represents the basic chemical transformation, identifying the reactants (starting substances) and the products (substances formed). However, in a skeletal equation, the number of atoms of each element is not the same on both the reactant (LHS) and product (RHS) sides. This means it does not follow the law of conservation of mass.

For example, the electrolytic decomposition of water has the skeletal equation:

\[ H_2O \rightarrow H_2 + O_2 \]

Here, oxygen atoms are not balanced.

A balanced chemical equation, like:

\[ 2H_2O \rightarrow 2H_2 + O_2 \]

has an equal number of atoms of each element on both sides, obeying the law of conservation of mass. While the skeletal equation shows what reacts and what is formed, the balanced equation also shows the correct proportions.