Available Answers

1. 1.

   Fill in the blanks.

   1. ______ are the substances that combine or react in a reaction.
   2. Calcium carbonates gives _____ and _____ on heating.
   3. Reactants that take place in the presence of light are called ______ reactions.
   4. Combination reactions are also called _____ reactions.
   5. When iron is heated with sulphur, ______ is formed. 
2. 2.

   Write True(T) or False(F).

   1. Chemical reactions can be represented using symbols and chemical formulae.
   2. The reactants are always written on the left-hand side in a chemical equation with a plus sign(+) between them.
   3. Liquid state is indicated by the symbol 'Iq' in a chemical equation.
   4. Any gas evolved during a reaction is represented by an arrow pointing upwards proceeding the chemical formula. 
   5. Skeletal equation has an equal number of atoms of one or more elements in the reactants and products. 
3. 3.

   Answer in one word/a few words.

   1. Substances formed in a reaction
   2. Another name for combination reaction
   3. A reaction in which compound splits into two or more simpler substances.
   4. A representation of a chemical reaction with the help of symbols and chemical formulae.
   5. Another name for an unbalanced equation
4. 4.

   Identify the error in the given statements, Circle the incorrect word and write the correct word in the blank.

   1. Reactions taking place in the presence of light are called photo reactions.
   2. Water dissociates into hydrogen and oxygen on passing light through it.
   3. A catalyst is a substance that changes the rate of a chemical reaction without itself undergoing any chemical change.
   4. Sodium sulphate decomposes to give sodium metal and chlorine gas.
   5. The products are always written on the left-hand side in a chemical equation. 
5. 5.

   Write the chemical equations for the following word equations.

   1. Magnesium ribbon or wire burns in air to form magnesium oxide.
   2. Hydrogen combines with chlorine to form hydrogen chloride.
   3. Iron is heated with sulphur to form iron sulphide.
   4. Calcium carbonate when heated decomposes to give calcium oxide and carbon dioxide. 
   5. Molten sodium chloride decomposes to give sodium metal and chlorine gas when electric current is passsed throught it. 
6. 6.

   1. Water dissociates into ____________ and ____________ on passing electricity through it.

   1. hydrogen, carbon
   2. hydrogen, oxygen
   3. hydrogen, sulphur
   4. hydrogen,nitrogen

   2. Which of the following is used as a catalyst in the decomposition of potassium chlorate (KCIO₃)?

   1. Potassium chloride
   2. Oxygen
   3. Sulphur dioxide
   4. Manganese dioxide

   3. _________ burns in air to form carbon dioxide and water.

   1. Fluorine
   2. Sodium
   3. Methane
   4. Nitrogen

   4. Which of the following combines with water to form carbonic acid?

   1. Carbon dioxide
   2. Carbon
   3. Hydrogen chloride
   4. Potassium

   5. ____________ on heating decomposes to give calcium oxide and carbon dioxide.

   1. Sodium Chloride
   2. Calcium Chloride
   3. Carbon Chloride
   4. Calcium Carbonate