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 Solution
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. Solution
(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
(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. Solution
(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.
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. Solution
(1)
(a) Physical change
(b) Chemical change
(c) Physical change
(d) Chemical change
(e) Physical change
(2) It is a chemical change as Iron react with dilute sulphuric acid to form Ferrous sulphate
(3) When iodine crystals are heated, the solid changes to the vapor state i.e., it sublimes. This is identified as a physical change since
(a) The vapors formed settle on the cooler parts of the test tube as solid - so the change is temporary and reversible.
(b) There is no change in mass.
(c) There is no energy (heat) change involved because the heat absorbed when the solid iodine changes to vapor, is given out when the vapor changes back to solid.
(d) The chemical composition of the solid is same as that of the vapor.
(4) When the candle burns, the heated wax melts. The melted wax re-solidifies and no new substance is formed, therefore this is a physical change. However, the wax and the wick continue to burn and produce new substances like carbon dioxide and water vapor. This burning process is a chemical change as it is a permanent change. Also, energy in the form of heat and light is evolved.
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. Solution
Zn + 2HBr -> ZnBr2 + H2
Zinc is solid reactant
Gaseous product formed is hydrogen
(2) What information is conveyed by a chemical equation?
(3) What information does the following equation convey?<
CaCO3 + 2HCI -> CaCI2 + H2O + CO2 Solution
One molecule of calcium carbonate reacts with two molecules of hydrochloric acid to produce one molecule each of calcium chloride, water and carbon dioxide
(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. Solution
(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.
