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 physics heat engine: second law of thermodynamics second law of thermodynamics the second law of thermodynamics second law of thermodynamic

Which statement is true about 2nd law of Thermodynamics?

  1. Heat can be converted to into work without changes in system or surroundings

  2. It is possible to construct a perpetual motion machine of second kind

  3. All spontaneous process are thermodynamically irreversible

  4. All spontaneous process are thermodynamically reversible
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

 2nd law of Thermodynamics states that all spontaneous process are irreversible 

Multiple choice physics heat engine: second law of thermodynamics second law of thermodynamics the second law of thermodynamics second law of thermodynamic

Which is not true for Second Law of Thermodynamics?

  1. The second law of thermodynamics states that the total entropy of an isolated system always increases over time, or remains constant in ideal cases where the system is in a steady state or undergoing a reversible process.

  2. It is impossible, by means of inanimate material agency, to derive mechanical effect from any portion of matter by cooling it below the temperature of the coldest of the surrounding objects.

  3. It is impossible to construct an engine which will work in a complete cycle, and produce no effect except the raising of a weight and cooling of a heat reservoir.

  4. The second law of thermodynamics states that the total energy of an isolated system is constant.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
The second law of thermodynamics states that the total entropy of an isolated system can never decrease over time. The total entropy can remain constant in ideal cases where the system is in a steady state (equilibrium), or is undergoing a reversible process. In all spontaneous processes, the total entropy always increases and the process is irreversible. The increase in entropy accounts for the irreversibility of natural processes, and the asymmetry between future and past.

Historically, the second law was an empirical finding that was accepted as an axiom of thermodynamic theory. Statistical mechanics, classical or quantum, explains the microscopic origin of the law.
Hence option D is only incorrect option.
Multiple choice chemistry group 17 group 17 - physical properties physical properties of group 17 elements group 17 elements: the halogen family

Change in entropy is negative for:

  1. $Bromine (I) \rightarrow Bromine (g)$
  2. $C(s)+H _2O(g) \rightarrow CO(g)+H _2(g)$
  3. $N _2(g, 10 \ atm) \rightarrow N _2(g, 1 \ atm)$
  4. $Fe(at \ 400 \ K) \rightarrow Fe(at \ 300 \ K)$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

When $Br(I)$ goes to to $Br(g)$ then stability of molecules increase. This leads us to negative entropy.

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

Which of the fallowing can enhance the rate of the reaction ?

  1. increasing the temperature

  2. increasing the concentration of products

  3. increasing the activation energy

  4. using a +Ve catalyst
Reveal answer Fill a bubble to check yourself
A,D Correct answer
Explanation

Solution:- (A) increasing the temperature and (D) using a +ve catalyst
  • Temperature is a measure of the kinetic energy of a system, so higher temperature implies higher average kinetic energy of molecules and more collisions per unit time. Hence an increase in temperature is accompanied by an increase in the reaction rate. 
  • A higher concentration of reactants leads to more effective collisions per unit time, which leads to an increased reaction rate (except for zero order reactions). Similarly, a higher concentration of products tends to be associated with a lower reaction rate.
  • Catalysts (e.g., enzymes) lower the activation energy of a chemical reaction and increase the rate of a chemical reaction without being consumed in the process. 
  • Hence, using a positive catalyst and increasing the temperature, both can enhance the rate of reaction.

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

What is the rate-determining step?

  1. The slowest step in the reaction.

  2. The fastest step in the reaction.

  3. The overall rate of the reaction.

  4. A law relating the steps of a reaction.

  5. The step which keeps on changing
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The slowest step in the mechanism of any reaction is the rate-determining step of the reaction.


Hence, the correct option is A.

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.