Tag: chemistry

Questions Related to chemistry

A chemical reaction in which heat is evolved is called a/an:

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

  1. exothermic reaction

  2. endothermic reaction

  3. thermite reaction

  4. catalytic reaction

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Correct Option: A
Explanation:

A reaction in which heat is released is called an exothermic reaction.

The reaction of nitrogen with oxygen to form nitric oxide is :

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

  1. Exothermic reaction

  2. Endothermic reaction

  3. Thermal balance reaction

  4. None of these

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Correct Option: B
Explanation:

Oxygen and nitrogen do not react at ambient temperatures. But at high temperatures, they undergo an endothermic reaction producing various oxides of nitrogen. Such temperatures arise inside an internal combustion engine or a power station boiler, during the combustion of a mixture of air and fuel, and naturally in a lightning flash.

Which may be correct for exothermic reaction?

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

  1. $\Delta H > {E _a}$

  2. $\Delta H < {E _a}$

  3. $\Delta H \ne {E _a}$

  4. All of these

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Correct Option: A
Explanation:
  • All chemical reactions, including exothermic reactions, need activation energy to get started. Activation energy is needed so reactants can move together, overcome forces of repulsion, and start breaking bonds.
  • If the molecules in the reactants collide with enough kinetic energy and this energy is higher than the transition state energy, then the reaction occurs and products form. In other words, the higher the activation energy, the harder it is for a reaction to occur and vice versa.
  • Hence by the above points we can conclude that $\Delta H>E _a$ for exothermic reaction.

Identify the following reactions as endothermic or exothermic.
(i) $2NaHCO _3+  {energy}\rightarrow Na _2CO _3+H _2O+CO _2$
(ii) $2Mg+O _2\rightarrow 2MgO+energy$

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

  1. (i) Exothermic (ii) Endothermic

  2. (i) Endothermic (ii) Exothermic

  3. (i) Exothermic (ii) Exothermic

  4. (i) Endothermic (ii) Endothermic

Show answer
Correct Option: B
Explanation:

Reaction with the absorption of energy is called an endothermic reaction.
In the reaction 

(i), Sodium Bicarbonate needs the energy to form sodium carbonate, water and carbon dioxide. 
Hence it is an endothermic reaction.
Reaction with the release of energy is called an exothermic reaction.
In the reaction 

(ii) on the burning of magnesium wire, magnesium oxide is formed by the release of energy in the form of heat and light.
Hence it is an exothermic reaction.

Which of the following process is exothemic in nature?

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

  1. Melting

  2. Boiling

  3. condensation

  4. Evaporation

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Correct Option: A

When ammonium chloride is dissolved in water, the solution becomes cold. 


The process is :

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

  1. exothermic

  2. endothermic

  3. super cooling

  4. None of these

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Correct Option: A

Limestone can be changed into slaked lime in two chemical reactions.
1 When limestone, $CaCO _{3}$, is heated it decomposes into lime, $CaO$.
2 Water is slowly dripped onto the cooled lime. The lime appears to expand and
steam is produced. Slaked lime, $Ca(OH) _{2}$, is formed.
Which row shows the correct description of each of the chemical reactions?

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

  1. Reaction $1$ - enodthermic, reaction $2$ - endothermic

  2. Reaction $1$ - enodthermic, reaction $2$ - exothermic

  3. Reaction $1$ - exothermic, reaction $2$ - endothermic

  4. Reaction $1$ - exothermic, reaction $2$ - exothermic

Show answer
Correct Option: B
Explanation:

Solution:- (B) Reaction $1$- endothermic, Reaction $2$- exothermic

When limestone is heated, the heat is absorbed and thus the reaction is endothermic and when steam is produced, the heat is released and thus the reaction is exothermic.

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

Show answer
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 .