Tag: endothermic and exothermic reactions

Questions Related to endothermic and exothermic reactions

Differentiate between an exothermic and an endothermic reaction.

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

  1. Endothermic releases heat and exothermic absorbs energy

  2. Exothermic releases heat and endothermic absorbs energy

  3. Hydrogen gas is evolved in exothermic but not in endothermic

  4. Hydrogen gas is evolved in endothermic but not in exothermic

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Correct Option: B
Explanation:

Exothermic reactions are reactions or processes that release energy, usually in the form of heat or light. In an exothermic reaction, energy is released because the total energy of the products is less than the total energy of the reactants.
Endothermic reactions are reactions that require external energy, usually in the form of heat, for the reaction to proceed. Since endothermic reactions draw in heat from their surroundings, they tend to cause their environments to cool down. They are also generally non-spontaneous since endothermic reactions yield products that are higher in energy than the reactants. As such, the change in enthalpy for an endothermic reaction is always positive. 


Hence, the correct option is $B$

In which of the following process heat is required?

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

  1. Mixing water and strong acids

  2. Some polymerisation reactions such as the setting of epoxy resin

  3. The setting of cement and concrete

  4. Combustion of fuels such as wood

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Correct Option: D
Explanation:

In combustion of fuels such as woods.

$C+O _2\longrightarrow CO _2+Heat$

Give an example of each of the following chemical changes: An endothermic reaction 

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

  1. making ice cubes

  2. condensation of rain from water vapor

  3. baking bread

  4. mixing sodium sulfite and bleach

Show answer
Correct Option: C
Explanation:

Exothermic reactions are reactions or processes that release energy, usually in the form of heat or light. In an exothermic reaction, energy is released because the total energy of the products is less than the total energy of the reactants.
When quick lime reacts with water to form slaked lime , it releases a lot of energy . 
Endothermic reactions are reactions that require external energy, usually in the form of heat, for the reaction to proceed. Since endothermic reactions draw in heat from their surroundings, they tend to cause their environments to cool down. They are also generally non-spontaneous, since endothermic reactions yield products that are higher in energy than the reactants. 
When hydrogen reacts with iodine to form hydrogen iodide , it absorbs a lot of energy .

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. $H \rightarrow H^-$

Show answer
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-}$

Show answer
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

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

Show answer
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

Show answer
Correct Option: A
Explanation:

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