Chemistry · Physics

Thermodynamics and Chemical Kinetics

1,092 Questions

Thermodynamics and chemical kinetics are crucial branches of physical chemistry. This area focuses on energy transformations, reaction rates, equilibrium constants, and catalysts. These topics carry significant weight in competitive science and engineering examinations.

Enthalpy and energyChemical equilibriumEntropy conceptsReaction kinetics and catalysts

Thermodynamics and Chemical Kinetics Questions

Multiple choice chemistry rates of reaction introduction to rate of reaction rate of chemical reaction rate of reaction

A gaseous phase reaction ${A _2} \to B + \frac{1}{2}C$ shows an increase in pressure from 100 mm to 120 mm in 5 min. Now, $ - \dfrac{{\Delta \left[ {{A _2}} \right]}}{{\Delta t}}$ should be:

  1. $8mm\,{\text{ - }}{\min ^{ - 1}}$
  2. $4mm\,{\text{ - }}{\min ^{ - 1}}$
  3. $16mm\,{\text{ - }}{\min ^{ - 1}}$
  4. $2mm\,{\text{ - }}{\min ^{ - 1}}$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Change in pressure $=120-100=20 mmHg$

Change in time $=5 min$
$\therefore$ Rate$=\cfrac{20}{5}mmHgmin^{-1}$
$=4mm\ Hg\ min^{-1}$

Multiple choice evs solar energy fuels and fossil fuels solar energy and its applications electric energy generation and environment

A chemical, when burned, produces energy if :

  1. The energy absorbed by product is more than the energy released by reactant.

  2. The energy absorbed by product is less than the energy released by reactant.

  3. The energy released by reactant is equal to energy absorbed by product.

  4. It reacts with carbon dioxide.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

A chemical reaction produces energy (exothermic) when the potential energy of the products is lower than that of the reactants, meaning the energy released by forming product bonds is greater than the energy absorbed to break reactant bonds.

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

Statement I: An exothermic reaction has a positive $\Delta H$.
Statement II: Heat must be added to the system for the reaction to occur.

  1. Statement 1 and Statement 2 are correct and Statement 2 is the correct explanation of Statement 1

  2. Both the Statement 1 and Statement 2 are correct and Statement 2 is NOT the correct explanation of Statement 1

  3. Statement 1 is correct but Statement 2 is not correct

  4. Statement 1 is not correct but Statement 2 is correct.

  5. Both the Statement 1 and Statement 2 are not correct.
Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

Option $E$ is the correct answer. Both the statements are incorrect.

In an exothermic reaction, heat is produced or given out when the reaction occurs.
And exothermic reaction has a negative delta $H$ value.

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

Which may be correct for exothermic reaction?

  1. $\Delta H > {E _a}$
  2. $\Delta H < {E _a}$
  3. $\Delta H \ne {E _a}$

  4. All of these
Reveal answer Fill a bubble to check yourself
A Correct answer
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.
Multiple choice chemistry endothermic and exothermic reactions endothermic reactions what are enthalpy changes energy change in chemical reactions

Differentiate between an exothermic and an endothermic reaction.

  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
Reveal answer Fill a bubble to check yourself
B Correct answer
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 $B$

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

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

  1. $F \rightarrow F^-$
  2. $Cl \rightarrow Cl^-$
  3. $O \rightarrow O^{2-}$
  4. $H \rightarrow H^-$
Reveal answer Fill a bubble to check yourself
C Correct answer
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.

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

In which of the following process energy is liberated:

  1. $ Cl \rightarrow Cl^+ + e^-$
  2. $ HCl \rightarrow H^+ + Cl^-$
  3. $ H^++e^- \rightarrow H$
  4. $ O + 2e^-\rightarrow O^{2-}$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Energy is liberated (exothermic) when an electron is added to an atom or ion (electron affinity). Option C represents the combination of a positive ion and an electron to form a neutral atom, which releases energy.

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

Select endothermic reaction:

  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
Reveal answer Fill a bubble to check yourself
B,C Correct answer
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 $C$

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

Select the correct alternative.

Which of the following reactions are exothermic in nature?

  1. Combustion of Carbon

  2. Bond breaking

  3. Bond formation

  4. Both (a) and (c)
Reveal answer Fill a bubble to check yourself
D Correct answer
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.

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

A chemical reaction in which energy is liberated is called:

  1. exothermic reaction

  2. endothermic reaction

  3. isothermal reaction

  4. physical change
Reveal answer Fill a bubble to check yourself
A Correct answer
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

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

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

  1. electrolysis of water.

  2. conversion of limestone into quicklime.

  3. process of respiration.

  4. process of photosynthesis.
Reveal answer Fill a bubble to check yourself
C Correct answer
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)






.

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

The formation of a larger chemical from the smaller components is known as 

  1. an endothermic reaction that requires energy

  2. an endothermic reaction that releases energy

  3. an exothermic reaction that requires energy

  4. an exothermic reaction that releases energy

  5. hydrolysis
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The internal energy of a larger chemical is smaller than that of the constituent ones. Hence energy is liberated when smaller components combine to form a large molecule. Hence the process is exothermic.

The correct answer is option D.

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

Which is a reaction that absorbs energy?

  1. Exothermic

  2. Particle Size

  3. Endothermic

  4. Catalyst

  5. Concentration
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The term endothermic process describes the process or reaction in which the system absorbs energy from its surroundings; usually, in the form of heat. The opposite of an endothermic process is an exothermic process, one that releases, "gives out" energy in the form of heat.