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Periodic Classification of Elements
What is a chemical equation? Illustrate with an example.
The mode of communicating facts in chemical language about a chemical reaction is called chemical equation. Thus, a chemical equation is an expression for given chemical change in terms of symbols or formula of the reactants and products. For example, the reaction of zinc with dilute sulphuric acid to produce zinc sulphate and hydrogen is given by the following chemical equation:
Zn + H2SO→ ZnSO4 + H2
In aobve reaction those are left-hand side is reactant and other part that is left hand side is product.
How will you know whether a chemical reaction has taken place?
When a chemical reaction occurs, one or more of the following changes take place :
(i) Change in state
(ii) Change in colour
(iii) Evolution of a gas
(iv) Change in temperature.
How would you justify that a chemical reaction has taken place in the following cases:
(i) Burning of magnesium ribbon in air.
(ii) Addition of lead nitrate solution to potassium iodide solution.
(iii) Addition of dilute hydrochloric acid to zinc granules.
(i) Burning of magnesium ribbon in air gives a powder (of MgO). So there is a change of state.
Magnesium + Oxygen --> Magnesium oxide(MgO)
(ii) Addition of colourless lead nitrate solution to potassium iodide solution gives yellow
coloured precipitate (lead iodide). So there is a change of colour.
(iii) Addition of dilute hydrochloric acid to zinc granules gives a gas (H2) with effervescence.
How do you show that respiration is a chemical change?
During respiration, energy is released.Respiration is a form of oxidation.
Glucose is oxidised to CO2 and H2O (along with release of energy) at the cells by the oxygen from air we breathe in.
C6H12O6 + 6O2 = 6CO2 + 6H2O+energy
Since glucose is converted into new products with different composition, respiration is a chemical change.
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