Tag: what are enthalpy changes

Questions Related to what are enthalpy changes

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.

Which of the following reaction is not endothermic in nature?

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

  1. breaking of bonds

  2. digestion of food

  3. combustion of Carbon

  4. evaporation of water

Show answer
Correct Option: C
Explanation:

Combustion or burning is a high temperature exothermic redox chemical reaction between fuel and an oxidant oxygen. Evaporation and sublimation are phase change physical process of water. Digestion of food is breakdown of larger molecules into small ones by bong breaking which is an endothermic process.

Select the correct alternative.

Which of the following reactions are exothermic in nature?

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

  1. Combustion of Carbon

  2. Bond breaking

  3. Bond formation

  4. Both (a) and (c)

Show answer
Correct Option: D
Explanation:

Combustion or burning is a high temperature exothermic redox chemical reaction between fuel and an oxidant oxygen. Bond breaking requires energy to be supplied for bond dissociation so it is an endothermic process while bond formation releases energy so that the product becomes stable which is an exothermic process.

Which of the following is an exothermic process?

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

  1. Dilution of sulphuric acid

  2. Sublimation of dry ice

  3. Evaporation of water

  4. Melting of ice

Show answer
Correct Option: A
Explanation:

A large amount of heat is released because the hydration reaction of sulfuric acid is highly exothermic and dilution should always be performed by adding the acid to the water rather than the water to acid. As hydration of sulfuric acid is thermodynamically favorable and the affinity of it for water is sufficiently strong.

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

Show answer
Correct Option: A
Explanation:

If you pour a few drops of petrol on your palm.it will feel cool as the petrol evaporates this is a endothermic reaction.Because petrol is very volatile in nature, so when it evaporates.it absorb heat energy from the surroundings.

A chemical reaction in which energy is liberated is called:

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

  1. exothermic reaction

  2. endothermic reaction

  3. isothermal reaction

  4. physical change

Show answer
Correct Option: A
Explanation:

Exothermic Reaction: This is a chemical reaction that releases energy through light or heat.

$CH _4+2O _2\rightarrow CO _2+2H _2O+\triangle$
Burning of $CH _4$ gas its produces $CO _2$ and water vapour and releases heat.
Endothermic Reaction: This is a chemical reaction which requires or absorbs energy from its surroundings usually in the form of heat.
$N _2+O _2\rightarrow 2NO$
$\triangle0=+180.5$kg

During the dissolution of urea, heat:

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

  1. is absorbed

  2. is evolved

  3. does not change

  4. none of the above

Show answer
Correct Option: A
Explanation:

During the dissolution of urea, heat is absorbed the term,dissolution,refers to a solute dissolving in a solvent to form a solution.In this experiment the solute is  solid urea.Urea being a molecular substance,does not dissociate into ions.The dissolution process involves adding energy to break the attractive forces between the molecules in the solid structure and releasing energy as the molecules form new attractive forces with the water molecules sourrounding it.

One of the following is an exothermic reaction. This is:

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

  1. electrolysis of water.

  2. conversion of limestone into quicklime.

  3. process of respiration.

  4. process of photosynthesis.

Show answer
Correct Option: C
Explanation:

(A)In electrolysis of water heat energy is used to convert water into hydrogen and oxygen.

$2H _2O\rightarrow2H _2+O _2$
 it is an endothermic reaction.

(B)conversion of limestone into quicklime can be done by heating limestone.
$CaCO _3\rightarrow CaO+CO _2$ it is an endothermic reaction.


(C)During respiration breakdown of glucose in presence of oxygen releases energy, therefore it is an exothermic process.
$C _6H _{12}O _6+6O _2\rightarrow6H _2O+6CO _2+energy$

(D)In process of photosynthesis- light energy is used to convert carbon dioxide and water into glucose and oxygen
$6CO _2+6H _2O\rightarrow C _6H _{12}O _6+6O _2$

So the answer is (c)






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