Tag: chemistry

Questions Related to chemistry

If you, pour a few drops of petrol on your palm, it will feel cool as the petrol evaporates. This change is a/an:

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

  1. endothermic reaction

  2. exothermic reaction

  3. chemical reaction

  4. slow reaction

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Correct Option: A

The process(es) requiring the absorption of energy is/are:

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

  1. $F \rightarrow F^-$

  2. $Cl \rightarrow Cl^-$

  3. $O \rightarrow O^{2-}$

  4. $H \rightarrow H^-$

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Correct Option: C
Explanation:

All the elements can easily gain an electron to form ions like $H^-$, $F^-$, $Cl^-$, and $O^{2-}$ atoms.

But, all the rest atoms except oxygen accepts only one electron, so they release energy and the value of electron gain enthalpy is negative.
But, oxygen first adds one electron where its first electron gain enthalpy is negative, but now the second electron is added to an anion, so that will require energy to add and hence the electron gain enthalpy becomes positive.
The answer is option C.

In which of the following process energy is liberated:

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

  1. $ Cl \rightarrow Cl^+ + e^-$

  2. $ HCl \rightarrow H^+ + Cl^-$

  3. $ H^++e^- \rightarrow H$

  4. $ O + 2e^-\rightarrow  O^{2-}$

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Correct Option: C

Select endothermic reaction:

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

  1. $S^{-}(g) + e^{-}(g) \rightarrow S^{2-}(g)$

  2. $Ne (g) + e^{-} (g) \rightarrow Ne^{-} (g)$

  3. $N(g) + e^{-} (g) \rightarrow N^{-}(g)$

  4. none of the above

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Correct Option: B,C
Explanation:

The following are examples of endothermic reactions. They have a positive value of electron gain enthalpy and energy is absorbed when an electron is added to the atom.

$\displaystyle  Ne (g) + e^{-} (g) \rightarrow Ne^{-} (g)$

$\displaystyle N(g) + e^{-} (g) \rightarrow N^{-}(g)$

The following is an example of an exothermic reaction. They have a negative value of electron gain enthalpy and energy is released when an electron is added to the atom.

$\displaystyle S^{-}(g) + e^{-}(g) \rightarrow S^{2-}(g)$.

So, the correct options are $B$ and $C$

Which of the following are exothermic processes?
(A) Reaction of water with quick lime
(B) Dilution of an acid
(C) Evaporation of water
(D) Sublimation of Camphor (Crystals)

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

  1. (a) and (b)

  2. (b) and (c)

  3. (a) and (d)

  4. (c) and (d)

Show answer
Correct Option: A
Explanation:

Addition of quick lime to water and dilution of acid are examples of exothermic reactions.
The addition of quick lime (CaO) to water gives a hissing sound and is known as slaking of lime. It is an exothermic reaction with release of 15000 cal/mol
$CaO + H _2O \rightarrow Ca(OH) _2 + 15000  : cal$
Conc sulfuric acid has very high affinity for water. When sulfuric acid is mixed with water, a large amount of hat is released. The temperature may rise to as high as $120^o  : C$.
Hence, sulfuric acid is always diluted by adding acid to water.
On the other hand, evaporation of water and sublimation of Camphor are endothermic processes.

Which of the following is not an endothermic reaction?

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

  1. $CaCO _3\rightarrow CaO+CO _2$

  2. $2H _2O\rightarrow 2H _2+O _2$

  3. $6CO _2+6H _2O\rightarrow C _6H _{12}O _6+6O _2$

  4. $C _6H _{12}O _6+6O _2\rightarrow 6CO _2+6H _2O$

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Correct Option: D
Explanation:

$C _6H _{12}O _6+6O _2\rightarrow 6CO _2+6H _2O$  is not endothermic reaction.
It is a synthesis reaction . the reaction is called cellular respiration as it produces energy for the body to use for activity. n oxidizing the glucose, the cell takes the energy from this chemical process and uses it for ATP synthesis. The ATP synthase is considered to be the most important carrier of energy in a cell. It captures energy, then uses that energy to fuel other processes within the cell. While most are formed during respiration, some are also made during photosynthesis.
Heat is not absorbed so it is not an endothermic reaction

The gas which is produced when sodium reacts with water:

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

  1. hydrogen

  2. oxygen

  3. water gas

  4. soda gas

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Correct Option: A
Explanation:

When sodium reacts with water sodium hydroxide is formed and hydrogen gas is evolved.$2Na+2H _2O\rightarrow2NaOH+H _2$

The process of respiration is:

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

  1. an oxidation reaction which is endothermic

  2. a reduction reaction which is exothermic

  3. a combination reaction which is endothermic

  4. an oxidation reaction which is exothermic

Show answer
Correct Option: D
Explanation:

The process of respiration is an oxidation reaction which is exothermic.
Respiration is considered as an exothermic reaction because in respiration oxidation of glucose takes place which produces large amount of heat energy. 

The reaction between carbon and oxygen can be represented as:
$C(g)\ + \ O _2(g)\rightarrow CO _{2}(g) + heat$
In which of the following type(s), the above reaction can be classified?
I. Combustion reaction
II. Displacement reaction 
Ill. Endothermic reaction
IV. Combination reaction

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

  1. (I) and (III)

  2. (I), (III) and (IV)

  3. (I) and (IV)

  4. (I) only

Show answer
Correct Option: C
Explanation:

$C(g)+O _2(g)\rightarrow CO _2(g)+heat$

As, the carbon is combining with oxygen to form $CO _2$, it is a combination reaction and the oxidation of carbon is also taking place in the presence of oxygen, it is also a combustion reaction.

When quickline is reacted with water, the reaction is:

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

  1. an endothermic reaction

  2. a reaction involving reduction

  3. an exothermic reaction

  4. a reaction involving oxidation

Show answer
Correct Option: C
Explanation:

Quicklime is reacted with water to form calcium hydroxide.

$CaO + H _2O\rightarrow Ca(OH) _2$
This reaction is exothermic reaction because some amount of heat evolved in the reaction.
So answer is C.