Tag: chemistry

Questions Related to chemistry

Which term means a reaction which releases energy?

chemistry endothermic and exothermic reactions endothermic reactions what are enthalpy changes energy change in chemical reactions

  1. Exothermic

  2. Particle Size

  3. Endothermic

  4. Catalyst

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Correct Option: A
Explanation:

An exothermic reaction is a chemical reaction that releases energy by light or heat. It is the opposite of an endothermic reaction. Expressed in a chemical equation: reactants → products + energy.

The dissolution in water of which of the following substances is endothermic?

chemistry endothermic and exothermic reactions endothermic reactions what are enthalpy changes energy change in chemical reactions

  1. Hydrochloric acid

  2. Sodium hydroxide

  3. Pure sodium

  4. Ammonium chloride

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Correct Option: D
Explanation:

(A) $HCl _{(l)}+H _2O _{(l)}\rightarrow HCl _{(aq)}+$ Heat (exothermic)

(B) $NaOH+H _2O\rightarrow Na^++OH^-+H _2O+$ Heat (exo)
(C) $Na _{(s)}+H _2O\rightarrow NaOH+$ Heat (exo)
(D) $AlCl _3+H _2O\rightarrow Al(OH) _3+3HCl$ (endo)

(D) is endothermic reaction.

The decomposition of vegetable into compost is an example of __________ reaction.

chemistry endothermic and exothermic reactions endothermic reactions what are enthalpy changes energy change in chemical reactions

  1. exothermic

  2. endothermic

  3. displacement

  4. none of these

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Correct Option: A
Explanation:

The decomposition of vegetable into compost is an example of  exothermic reaction.

The decomposition of vegetable matter into useful compost is carried out by microbes.These reactions involve break down of bonds.The overall reaction is exothermic.

$Si + C \rightarrow$ SiC. This chemical reaction is an example for:

chemistry endothermic and exothermic reactions endothermic reactions what are enthalpy changes energy change in chemical reactions

  1. exothermic reaction

  2. endothermic reaction

  3. dissociation reaction

  4. displacement reaction

Show answer
Correct Option: A
Explanation:

$Si + C \rightarrow SiC$.

This chemical reaction is an example of an exothermic reaction as heat is liberated during the reaction. It is also an example of a combination reaction. Two elements combine to form a single compound.

To start, every biochemical reaction is:

chemistry endothermic and exothermic reactions endothermic reactions what are enthalpy changes energy change in chemical reactions

  1. exergonic

  2. endergonic

  3. both $A$ and $B$

  4. none of the above.

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Correct Option: B
Explanation:

Since any chemical reaction requires some energy of activation to start with, so this step is endergonic or since biochemical reaction is also a type of chemical reaction, so its first step is endothermic or endergonic.

A solution of 500 ml of 0.2 M KOH and 500 ml of 0.2 M HCl is mixed and stirred; the rise in temperature is $T _1$. The experiment is repeated using 250 ml of each solution, the temperature raised is $T _2$. Which of the following is true :

chemistry endothermic and exothermic reactions endothermic reactions what are enthalpy changes energy change in chemical reactions

  1. $T _1=T _2$

  2. $T _1=2T _2$

  3. $T _1=4T _2$

  4. $T _2=9 T _1$

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Correct Option: A

The following is (are) endothermic reaction(s) :

chemistry endothermic and exothermic reactions endothermic reactions what are enthalpy changes energy change in chemical reactions

  1. Combustion of methane.

  2. Decomposition of water

  3. Dehydrogenation of ethane to ethylene.

  4. Conversion of graphite to diamond.

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Correct Option: B,C,D
Explanation:

Combustion reaction are exothermic, hydrogenation of alkenes are exothermic and graphite is thermodynamically more stable.

During the reaction of some metals with dilute hydrochloric acid, the following observations were made. The temperature of the reaction mixture rises when aluminium (Al) is added mainly because :

                       

chemistry endothermic and exothermic reactions endothermic reactions what are enthalpy changes energy change in chemical reactions

  1. Heat is evolved

  2. Due to the catalyst

  3. It is an endothermic reaction.

  4. It is an exothermic reaction.

Show answer
Correct Option: A,D
Explanation:

The temperature of the reaction mixture rises beacause, the following exothermic reaction takes place:

$2Al(s)  +  6HCl(aq)  \rightarrow   2AlCl _{3}(aq)  +  3H _{2}(g)  +  heat$

Decomposition of ferrous sulphate is a/an:

chemistry endothermic and exothermic reactions endothermic reactions what are enthalpy changes energy change in chemical reactions

  1. precipitation reactions

  2. exothermic reactions

  3. endothermic reactions

  4. Synthesis reactions

Show answer
Correct Option: C
Explanation:

Decomposition of ferrous sulphate is an endothermic reaction as it involves absorption of heat to form ferric oxide ($Fe _{2}O _{3}$), sulphur dioxide ($SO _{2}$) and sulphur trioxide ($SO _{3}$). The equation for this reaction can be written as:
$ 2FeSO _{4}(s)  \overset{heat}{\rightarrow}  Fe _{2}O _{3}(s)  +  SO _{2}(g)  +  SO _{3}(g)$

During the reaction of some metals with dilute hydrochloric acid,
following observations were made. 
 
The reaction of sodium metal is found to be highly explosive because:

chemistry endothermic and exothermic reactions endothermic reactions what are enthalpy changes energy change in chemical reactions

  1. Heat is evolved

  2. Due to the catalyst

  3. It is an endothermic reaction.

  4. It is an exothermic reaction.

Show answer
Correct Option: A,D
Explanation:

Reaction of sodium with hydrochloric acid is highly exothermic one and therefore explosive in nature.
$2Na(s)  +  2HCl(aq)  \rightarrow   2NaCl(aq)  +  H _{2}(g)$  +  heat