chemical reactions and equations class 10 questions answers

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One Marks Questions

(1) Define a chemical change.
(2) Give four examples of a chemical change.
(3) Give four characteristics of a physical change.
(4) Give an example of a chemical change that is reversible.
(5) Define a physical change.
(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
(7) Give four examples of a physical change.
(8) Give four characteristics of a chemical change.
(9) What do you understand by an exothermic chemical change

Two Marks Questions

Explain whether the following are physical or chemical changes. Give one reason for your answer.
(1) Formation of curd
(2) Ripening of fruit
(3) Bending a glass tube by heating
(4) Melting of wax
(5) Formation of wine
(6) Action of heat on blue vitriol is a physical as well as chemical change. Justify.
(7) Is boiling of water, a chemical change? Give reason for your answer.
(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.
(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.

True and False statement

(1)Chemical changes are generally accompanied by an exchange of energy.
(2)A physical change is usually reversible.
(3) When a magnesium ribbon burns brilliantly in air a physical change takes place.
(4)Ammonium chloride dissolves in water with the absorption of heat. This is an exothermic.

One Marks Questions

(1) Identify physical or chemical changes in the following:
(a) A rock rolls down a slope
(b) Baking of cake
(c) Plucking of fruit
(d) Burning of L.P.G
(e) Cutting of carrots
(2) Explain whether the addition of dilute sulphuric acid to iron is a physical or chemical change.
(3) Heating of iodine crystals is considered to be a physical change. Explain.
(4) Burning of a candle may be considered as showing physical and chemical changes occurring simultaneously. Explain.

Four Marks Questions

(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.

(2) What information is conveyed by a chemical equation?
(3) What information does the following equation convey?< CaCO3 + 2HCI -> CaCI2 + H2O + CO2

(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.

(5) Define the following terms
(a) Thermal decomposition
(b) Electrolytic decomposition
(6) What type of reaction is this? Why is it called so?
NaOH (aq) + HCI (aq)—NaCI (aq) + H2O (I)

(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
(8) When an iron knife is dipped in a solution of copper sulphate, a reddish brown layer gets formed on the knife. Explain.
(9) When hydrochloric acid is converted to chlorine, is the acid getting oxidized? Explain.
(10) Ammonium nitrate when heated disappears completely. Why?
(11) Chemical reactions are often accompanied by heat changes. Explain.
(12) State what type of reaction the following are:
(a) Splitting of water into hydrogen and oxygen
(b)burning of hydrogen in air
(c) Action of iron with copper sulphate solution
(d) Action of  heat on calcium carbonate
(e) Treating silver nitrate with hydrochloric acid
(13) When ice is exposed to air, it melts to form water and when hydrogen in burnt in air, it forms water. How do these changes differ?
(14) Blue Copper Nitrate crystals turns black when heated. Explain.
(15) When chlorine is passed through potassium iodine solution containing chloroform, purple color is observed. Explain.
(16) When silver nitrate is added to seawater, a white precipitate is formed. Explain.
(17)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. (18) 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? (19)What is a redox reaction? Write down a chemical equation representing it. (20)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

(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
(2) Define a double decomposition reaction
(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
(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.
(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?
(6)Mention three ways by which a usual chemical equation can be made more informative.
(7)What is meant by skeletal chemical equation? What does it represent? Using the equation for electrolytic decomposition of water, differentiate between a skeletal chemical equation and a balanced chemical equation.

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Practice Question

Question 1 Which among the following is not a base?
B) $NH_4OH$
C) $C_2H_5OH$
Question 2 What is the minimum resistance which can be made using five resistors each of 1/2 Ohm?
A) 1/10 Ohm
B) 1/25 ohm
C) 10 ohm
D) 2 ohm
Question 3 Which of the following statement is incorrect? ?
A) For every hormone there is a gene
B) For production of every enzyme there is a gene
C) For every molecule of fat there is a gene
D) For every protein there is a gene

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