Class 10 Science Chapter 1 Question Answer | Important Questions & Test Paper (2025)
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Multiple Choice Questions
Question 1. Which of the following equations represents a double displacement reaction?
(a) \(2H_2 + O_2 \rightarrow 2H_2O\)
(b) \(2HgO \rightarrow 2Hg + O_2\)
(c) \(Zn + CuSO_4 \rightarrow ZnSO_4 + Cu\)
(d) \(AgNO_3 + NaCl \rightarrow AgCl + NaNO_3\)
Question 2. Which of the following equations represents an exothermic reaction?
(a) \(2H_2 + O_2 \rightarrow 2H_2O\)
(b) \(2HgO \rightarrow 2Hg + O_2\)
(c) \(Zn + CuSO_4 \rightarrow ZnSO_4 + Cu\)
(d) \(AgNO_3 + NaCl \rightarrow AgCl + NaNO_3\)
Question 3. What is the product of the combination reaction between hydrogen and oxygen?
(a) Hydrogen Peroxide
(b) Water
(c) Hydrogen Chloride
(d) Oxygen Difluoride
Question 4. In the reaction \(2H_2 + O_2 \rightarrow 2H_2O\), what is the reactant?
(a) Water
(b) Hydrogen
(c) Oxygen
(d) Both Hydrogen and Oxygen
Question 5. In the reaction $V2O5 + 5Ca -> 2V + 5CaO, what is the oxidizing agent?
(a) Ca
(b) V
(c) V2O5
(d) Both V2O5 and Ca
Question 6. Which of the following statements about the given reaction are correct?
3Fe(s) + 4H2O(g) -> Fe3O4(s) + 4H2(g)
(i) Iron metal is getting oxidised
(ii) Water is getting reduced
(iii) Water is acting as reducing agent
(iv) Water is acting as oxidising agent
(a) (i), (ii) and (iii)
(b) (iii) and (iv)
(c) (i), (ii) and (iv)
(d) (ii) and (iv)
Answer
1. (d),
2. (a),
3. (b),
4. (d),
5. (a),
6. (c) The substance which oxidises the other substances in a chemical reaction is known as an oxidising agent. Likewise, the substance which reduces the other substance in a chemical
reaction is known as reducing agent
One Marks Questions
Question 1. Define a chemical change. Question 2. Give four examples of a chemical change. Question 3. Give four characteristics of a physical change. Question 4 What are reactants in a chemical reaction? Question 5. Define a physical change. Question 6. Classify as physical or chemical change:
(i) Tearing of paper
(ii) Production of biogas
(iii) Butter going rancid
(iv) Magnetization of iron
(v) Clotting of blood
Question 7. Give four characteristics of a chemical change. Question 8. What do you understand by an exothermic chemical change
Answer
A chemical change is when the nature and identity of the initial substance change, and a chemical reaction takes place.
* Milk left at room temperature during summers
* Iron exposed to humid atmosphere
* Grapes get fermented
* Food is cooked
Here are four characteristics of a physical change:
1. No new substance is formed.
2. It is usually reversible.
3. Only physical properties (e.g., shape, size, state) are altered.
4. Energy changes, if any, are minimal.
Reactants are the substances that undergo chemical change in a reaction
A physical change is a process where a substance undergoes a transformation in its physical properties, such as shape, size, state, or appearance, without altering its chemical composition. For example, melting ice into water is a physical change, as the substance remains H₂O throughout.
Here are four characteristics of a chemical change:
1. New substances are formed.
2. It is often irreversible.
3. Energy changes, such as heat or light, are involved.
4. Chemical composition and properties of the substance change.
An exothermic chemical change is a reaction in which heat is released along with the products.
Two Marks Questions
Explain whether the following are physical or chemical changes. Give one reason for your answer. Question 1. Formation of curd Question 2. Ripening of fruit Question 3. Bending a glass tube by heating Question 4. Melting of wax Question 5. Formation of wine Question 6. Action of heat on blue vitriol is a physical as well as chemical change. Justify. Question 7. Is boiling of water, a chemical change? Give reason for your answer. Question 8. A person eats chocolate and then digests it. In doing so a physical and a chemical change takes place. Identify the changes and give reasons for your answer. Question 9. When we mix iron filings with sulfur and grind it, a physical change takes place. However, if we heat the mixture, a chemical change takes place. Explain why the former is said to be a physical change while the latter process is said to be a chemical change.
Answer
(1) Chemical change as lactic acid is formed (2) chemical change (3) Physical change (4) Physical change (5) Chemical change (6) When blue vitriol is heated,it loses it moisture , turns into white power. If we add water again, it again converts into blue color. So physical change
Now when it is strongly heated, Copper Sulphate decomposes into Copper oxide and suphur dioxide.So it is a chemical change (7) Boiling of water is a physical change as new substance is formed and steam when cooled again get converted into water (8) When the person chews the chocolate and breaks it into smaller pieces - it is a physical change. No new substances have been formed as yet. Once acted upon by saliva and other digestive juices, the chocolate is broken down into other simpler substances, which can be absorbed by the blood. This is a chemical change. (9) Mixing iron filings with sulfur is considered to be a physical change because the mixture can be easily separated and no new substance is formed. Moreover, no energy changes occur while mixing iron and sulfur. When the mixture is heated, the two substances combine to form a new substance known as ferrous sulphide. The original substance, iron and sulfur, cannot be re-obtained by cooling the ferrous sulphide. Consequently, it is a permanent chemical change involving an energy change.
True and False statement
Question 1.Chemical changes are generally accompanied by an exchange of energy. Question 2.A physical change is usually reversible. Question 3. When a magnesium ribbon burns brilliantly in air a physical change takes place. Question 4.Ammonium chloride dissolves in water with the absorption of heat. This is an exothermic.
Answer
(1) True
(2) True
(3) False Correct statement: When a magnesium ribbon burns brilliantly in air a chemical change takes place.
(4) False Correct statement: Ammonium chloride dissolves in water with the absorption of heat. This is an endothermic reaction.
Four Marks Questions
Question 1. Given the following equation:
Zinc+ Hydro bromic acid----Zinc bromide + Hydrogen
(i)Write the equation using symbols and formula.
(ii)Name a solid reactant in the reaction.
(iii) Name a gaseous product formed in the reaction.
Answer
Zn + 2HBr -> ZnBr2 + H2
Zinc is solid reactant
Gaseous product formed is hydrogen
Question 2. What information is conveyed by a chemical equation? Question 3. What information does the following equation convey?<
CaCO3 + 2HCI -> CaCI2 + H2O + CO2
Answer
One molecule of calcium carbonate reacts with two molecules of hydrochloric acid to produce one molecule each of calcium chloride, water and carbon dioxide
Question 4. Balance the following equations after writing them as molecular equations.
(a)Sodium + Nitrogen -> Sodium nitride
(b) Aluminum + Chlorine -> Aluminum chloride
(c)Iron (III) oxide + Hydrogen ->Iron + Water
(d) Phosphorous + oxygen -> Phosphorus pentoxide
(e) Trilead tetra oxide-> Lead monoxide + Oxygen.
Question 5. Define the following terms
(a) Thermal decomposition
(b) Electrolytic decomposition Question 6. What type of reaction is this? Why is it called so?
NaOH (aq) + HCI (aq)—NaCI (aq) + H2O (I)
Question 7. Give the balanced equation for reactions that take place when the following are heated
(a)Silver oxide
(b) Potassium nitrate
(c)Lead nitrate
(d) Trilead tetraoxide
(e) Copper carbonate Question 8. When an iron knife is dipped in a solution of copper sulphate, a reddish brown layer gets formed on the knife. Explain. Question 9. When hydrochloric acid is converted to chlorine, is the acid getting oxidized? Explain. Question 10. Ammonium nitrate when heated disappears completely. Why? Question 11. Chemical reactions are often accompanied by heat changes. Explain. Question 12.Consider the following chemical reaction:
X + Water----- Slaked lime
(a) Write the chemical name of ‘X’ and the type of reaction that occurs.
(b) Write chemical equation of the reaction. Question 13. A small amount of ferrous sulphate were heated in a hard glass test tube.
(i) Write the equations involved in the reaction.
(ii) What type of reaction is taking place? Question 14.What is a redox reaction? Write down a chemical equation representing it. Question 15.What change will you observe if white silver chloride is placed in sunlight? Write an equation for the reaction and the type of reaction.
Five Marks Questions
Question 1. Write chemical reaction for these
(a) Treating dilute sulphuric acid with sodium hydroxide solution
(b) Heating ammonium chloride
(c) Changing ammonium chloride into sodium and chlorine
(d) Heating a mixture of iron and sulfur
(e) Passing chlorine through a solution of potassium bromide Question 2. Define a double decomposition reaction Question 3. What type of change takes place in the following, physical or chemical? Briefly explain.
(a) Heating of zinc oxides
(b) Action of sodium with water
(c) Rain cycle
(d) Heating calcium carbonate
(e) Action of dilute acids on magnesium Question 4. Name the following and give equations for these reactions:
(a) A white solid, which when heated, leaves behind a yellow solid and gives CO2.
(b) A bluish green powder, on heating, leaves behind a black solid and gives CO2.
(c) A colorless solid produces a yellow solid when hot and a white solid when cold and gives a reddish brown gas. Give equations for each. Question 5.In the electrolysis of water,
(a) Name the gas collected at the cathode and anode.
(b) Why is the volume of gas collected at one electrode double the other?
(c) Why is a few drops of dil. H2SO4 added to the water?
Summary
This chemical reactions and equations class 10 questions answers is prepared keeping in mind the latest syllabus of CBSE . This has been designed in a way to improve the academic performance of the students. If you find mistakes , please do provide the feedback on the mail.
