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CHEMISTRY [2 Mark Question Answer]

Physical and Chemical Changes · ICSE STD 7 (ICSE - English Medium). 13 questions.

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[2 Mark Question Answer]

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13 questions · timed · auto-graded

Question 12 Marks
Write balanced chemical equation :
An aqueous calcium hydroxide solution (lime water) reacts with carbon dioxide gas to produce calcium carbonate and water.
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Question 52 Marks
Write chemical equations in symbols.
iron + sulphur → iron (II) sulphide
Answer
$\underset{\text { carbon }}{ Fe }+\underset{\text { sulphur }}{ S } \xrightarrow{\text { heat }} \underset{\text { iron(II) sulphide }}{ FeS }$
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Question 62 Marks
complete chemical equation balance them : $\text{H}_2 +$ _________ $\rightarrow \text{HCl}$
Answer
$\text{H}_2 + \text{Cl}_2 \rightarrow \text{HCl}$
Element $\text{LHS}$ $\text{RHS}$
$\text{H}$ $2$ $1$
$\text{Cl}$ $2$ $1$
Multply $\text{HCl}$ in $\text{RHS}$ by $2$ to balance both $\text{H}$ and $\text{Cl}$ atoms.
$\text{H}_2 + \text{Cl}_2 \rightarrow 2\text{HCl}$
Element $\text{LHS}$ $\text{RHS}$
$\text{H}$ $1$ $2$
$\text{Cl}$ $2$ $2$
Now the equation is balanced.
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Question 72 Marks
complete chemical equation balance them : $\text{Mg} + \text{O}_2 \rightarrow $ __________
Answer
$\text{Mg} + \text{O}_2 \rightarrow \text{MgO}$
Element $\text{LHS}$ $\text{RHS}$
$\text{Mg}$ $1$ $1$
$\text{O}$ $2$ $1$
Multply $\text{MgO}$ on $\text{RHS}$ by $2$ to balance the oxygen atoms.
$\text{Mg} + \text{O}_2 \rightarrow \text{MgO}$
Element $\text{LHS}$ $\text{RHS}$
$\text{Mg}$ $1$ $2$
$\text{O}$ $2$ $2$
Now, multply Mg on $\text{LHS}$ to balance $\text{Mg}$ atoms.
$2\text{Mg} + \text{O}_2 + 2\text{MgO}$
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Question 82 Marks
complete chemical equation balance them : $\text{AgCl} \rightarrow $ _________ $+ \text{Cl}_2$
Answer
$\text{AgCl} \rightarrow \text{Ag} + \text{Cl}_2$
Element $\text{LHS}$ $\text{RHS}$
$\text{Ag}$ $1$ $1$
$\text{Cl}$ $1$ $2$
Multply $\text{AgCl}$ on $\text{LHS}$ by $2$ to balance the $\text{Cl}$ atoms.
$2\text{AgCl} \rightarrow \text{Ag} + \text{Cl}_2$
Element $\text{LHS}$ $\text{RHS}$
$\text{Ag}$ $2$ $2$
$\text{Cl}$ $2$ $1$
Multply $\text{Ag}$ on $\text{RHS}$ by $2$ to balance the $\text{Ag}$ atoms.
$2\text{AgCl} \rightarrow 2\text{Ag} + \text{Cl}_2$
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Question 92 Marks
complete chemical equation balance them : $\text{N}_2 +$ _______ $\rightarrow \text{NO}$
Answer
$\text{N}_2 + \text{O}_2 \rightarrow \text{NO}$
Element $\text{LHS}$ $\text{RHS}$
$\text{N}$ $2$ $1$
$\text{O}$ $2$ $1$
Multiply $\text{NO}$ by $2,$ we get
$\text{N}_2 + \text{O}_2\rightarrow \text{NO}$
Element $\text{LHS}$ $\text{RHS}$
$\text{N}$ $2$ $2$
$\text{O}$ $2$ $2$
Since the number of atoms of each element is equal on both sides, it is balanced now.
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Question 102 Marks
What is a chemical equation ?
Answer
The representation of a chemical reaction by using the symbols and formulae of the reactants and the products involved in the reaction is called its chemical equation.
Example :
$\text{C} \ ($carbon$)\  + \ \text{O}_2 \rightarrow \text{CO}_{2}$
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Question 112 Marks
Why is the burning of paper a chemical change ?
Answer
If we bum a piece of paper, new substances like carbon dioxide, water vapour, smoke and ash are produced. The molecules of paper and oxygen combine and undergo changes to form molecules of these new substances. The change is permanent and cannot be reversed. Thus, the burning of paper is a chemical change.
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Question 122 Marks
What is a chemical change ?
Answer
A chemical change is a permanent change in which the original substance loses its own composition and properties and give rise to one or more new substances.
Examples : Rusting of iron, digestion of food, ripening of fruits, etc.
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Question 132 Marks
What is a physical change ?
Answer
A physical change is a temporary change in which no new substance is formed, and the chemical composition of the original substance is not altered. Examles : melting of wax, freezing of water, breaking a chalk piece, etc.
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[2 Mark Question Answer] - CHEMISTRY STD 7 Questions - Vidyadip