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Question : 30
Total: 39
With the help of an appropriate example, justify that some of the chemical reactions are determined by
(a) Change in temperature.
(b) Evolution of a gas, and
(c) Change in colour
Give chemical equation for the reaction involved in each case.
(a) Change in temperature.
(b) Evolution of a gas, and
(c) Change in colour
Give chemical equation for the reaction involved in each case.
Solution:
Change in temperature: Some chemical reactions are characterised by change of temperature such as addition of water to quicklime produces slaked lime and a lot of heat. As a result, the temperature of the reaction mixture increases. Thus, change in temperature indicates that a chemical reaction has taken place.
CaO + H 2 O → Ca ( OH ) 2 + Heat
(b) Evolution of a gas: The chemical reaction between zinc and dilute sulphuric acid is characterised by the evolution of hydrogen gas.
Zn ( s ) + H 2 SO 4 ( a q ) → ZnSO 4 ( s ) + H 2 ( g )
(c) Change in colour: The reaction between lead nitrate solution and potassium iodide solution.
Pb ( NO 3 ) 2 ( a q ) + 2 KI → PbI 2 ( s ) + 2 KNO 3 ( a q )
In this reaction colour changes from colourless to yellow.
(b) Evolution of a gas: The chemical reaction between zinc and dilute sulphuric acid is characterised by the evolution of hydrogen gas.
(c) Change in colour: The reaction between lead nitrate solution and potassium iodide solution.
In this reaction colour changes from colourless to yellow.
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