Chemistry · Physics

Thermodynamics and Chemical Kinetics

1,132 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

${H} _{2}(g)+{I} _{2}(g)+51.9\ kilojoules\rightarrow 2HI(g)$
Which of the following can be expected to increase the rate of the reaction given by the equation above?
$I$. Adding some helium gas
$II$. Adding a catalyst
$III$. Increasing the temperature

  1. $I$ only
  2. $III$ only
  3. $II$ only
  4. $II$ and $III$ only
  5. $I,II$ and $III$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

(i)   Addition of Helium gas will not increase the rate of reaction. It will either remain same or decrease depending upon 

      whether addition is done in constant volume or constant pressure conditions.
(ii)  Adding a catalyst will lower the activation energy and thus increase the value of the rate constant which will increase the rate.
(iii)  Increasing the temperature will also increase the value of rate constant and thus the rate of the reaction will increase.
                       $K=A{ e }^{ -Ea/RT }$
$\therefore $ only (ii) & (iii).

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

The rate of reaction for a concentrated strong acid with a concentrated strong base is least affected by which of the following?

  1. The use of a catalyst.

  2. A change in temperature.

  3. A change in reactant concentration.

  4. A change in pressure.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

A change in pressure effects only if there is a difference between the number of moles of gaseous products & the number of moles of gaseous reactant. In short, a change in pressure affects only if there is at least one gas either in products or reactants. 

Reaction could be such as:


$ HCl(aq) + NaOH (aq) \rightarrow  NaCl(aq) + H _2O (l)$

As the reaction between concentrated acid and a base reactant or product takes place, there is least effect of change in pressure on the rate of reaction.

Hence, the correct option is D.


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

Which factor has no influence on the rate of reaction?

  1. Molecularity

  2. Temperature

  3. Concentration of reactant

  4. Nature of reactant
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Molecularity is a theoretical concept describing the mechanism of an elementary step, whereas the rate of a reaction is an experimental observation influenced by external factors like temperature, concentration, and catalysts.

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

Negative sign denotes that the concentration of reactant is                     with time.

  1. decreasing

  2. increasing

  3. heating up

  4. cooling up
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The speed of a chemical reaction may be defined as the change in concentration of a substance divided by the time interval during which this change is observed. Definition of a rate of reaction. We, in general, use a negative sign for reactants because its concentration is decreasing as the chemical reaction is taking place.

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

The rate of reaction usually decreases with time.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The speed of a chemical reaction may be defined as the change in concentration of a substance divided by the time interval during which this change is observed. Hence rate of reaction is inversely related as the time increases rate of reaction decreases. Hence given statement is true.

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

Which does not affect the rate of a reaction?

  1. Nature of the reactants

  2. Time

  3. Concentrations

  4. Surface area exposed

  5. Temperature
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Time does not affect the rate of a reaction. Hence, in the rate law expression $ \displaystyle rate = k[A]^n$, there is no term for time.
Nature of the reactants, Concentrations, surface area exposed and temperature affects  the rate of a reaction.

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.