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Chemical Changes and Reactions
Complete the following statements:
- The chemical change involving iron and hydrochloric acid illustrates a _________________ reaction.
- In the type of reaction called_______________, two compounds exchange their positive and negative radicals.
- A catalyst either ______ or _____________ the rate of a chemical change but itself remains ______________ at the end of the reaction.
- On heating, hydrated copper sulphate changes its colour from ________ to __________.
Displacement
,Double decomposition
,Accelerates, decelerates, unaffected
,Blue, white
When hydrogen burns in oxygen, water is formed; when electricity is passed through water, hydrogen and oxygen are given out. Name the type of chemical change involved in the two cases.
When hydrogen burns in oxygen, water is formed - Combination Reaction.
When electricity is passed through water, hydrogen and oxygen are given out - Decomposition Reaction.
Explain, giving one example for each of the following chemical changes:
(a) Double decomposition
(b) Thermal decomposition
(c) Reversible reaction
(d) Displacement
(a) Double decomposition: This is a type of chemical change in which two compounds in a solution react to form two new compounds by mutual exchange of radicals.
(b) Thermal decomposition
A decomposition reaction brought about by heat is known as thermal decomposition.
2HgO(s) 
2Hg(s) +O2(g)
(c) Reversible reaction
A chemical reaction in which the direction of a chemical change can be reversed by changing the conditions under which the reaction is taking place is called a reversible reaction.
CuSO4.5H2O(s) ⇋ CuSO4(s) + 5H2O(g)
(d) Displacement
It is a chemical change in which a more active element displaces a less active element from its salt solution.
CuSO4 + Zn → ZnSO4 + Cu
(a) What is synthesis?
(b) What kind of chemical reaction is synthesis? Support your answer by an example.
combination reaction.
A + B → AB
In the above reaction, substances A and B combine to give a molecule of a new substance, AB.
Carbon burns in oxygen to form a gaseous compound, carbon dioxide.
C + O2
CO2
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Mock Test Series
Mock Test Series