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 physics types of energy law of conservation of energy the law of conservation of energy work, energy and machines

According to the law of conservation of energy.

  1. energy exists in only one form

  2. energy can be created but no destroyed, and it can be transformed from one form to another

  3. energy exists in many forms but it cannot be transformed

  4. energy can neither be produced nor be destroyed, it can only be transformed from one form to another form
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Law of conservation of energy.

Multiple choice physics types of energy law of conservation of energy the law of conservation of energy work, energy and machines

Law of conservation of energy states that :

  1. energy cannot be destroyed but can be created and transformed from one form to another

  2. enerry exists in only one form

  3. energy exists in many forms but it cannot be transformed

  4. energy can neither be created nor be destroyed but can be transformed from one form to another
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The law of conservation of energy states that energy can neither be created nor be destroyed but it can be converted from one form to another i.e total energy in the universe will never change.

Eg:- Potential energy of a gas or oil is changed into energy to heat a building.

Multiple choice hmp shunt alternative to glycolysis carbohydrate metabolism respiration bio-chemistry
Last ${e}^{-}$ acceptor during ETS is 
  1. ${O} _{2}$
  2. cyt $a$
  3. cyt ${a} _{2}$
  4. cyt ${a} _{3}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

In electron transport chain, there are 7 electron acceptors, which are as follows $Co-Q\rightarrow Cyt\,\, b\rightarrow Cyt \,\,{c} _{1} \rightarrow Cyt \,\,c\rightarrow Cyt \,\,a\rightarrow Cyt \,\,{a} _{3}\rightarrow{O} _{2}$. Oxygen is the ultimate electron acceptor. These electron acceptors are present in a specific sequence along inner mitochondrial membrane.

Multiple choice chemistry chemical kinetics collision theory collision theory of chemical reactions rate of chemical reaction

On increasing the temperature by $10^{0}$C:

  1. number of collisions get doubled

  2. value of rate constant does not change

  3. energy of activation increases

  4. number of fruitful collisions gets doubled
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Increasing the temperature of the substance, increases the fraction of molecules which collide with energies greater than $Ea$. For every $10^0 C$ rise in temperature, the fraction of molecules having energy equal to or greater than Ea gets doubled leading to doubling the rate of reaction.

Hence, the number of fruitful collisions gets doubled.

Multiple choice chemistry how far? how fast? collision theory collision theory of chemical reactions rate of chemical reaction

What happen with the rate of the reaction when the frequency and the number of effective collisions between reacting particles increases?

  1. Increases

  2. Decreases

  3. Remains the same

  4. Approaches zero

  5. None of the above
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The atoms, ions and molecules can react to form products when they collide with enough kinetic energy and at favorable orientation. On increasing the frequency and the number of effective collisions between reacting particles increases the chance of reactants to come together to form a product  that results in the increase of rate of the reaction. 

Multiple choice chemistry how far? how fast? collision theory collision theory of chemical reactions rate of chemical reaction

What causes an increase in effective collisions without increasing average energy?

  1. An increase in the reactant concentration

  2. An increase in the temperature

  3. A decrease in pressure

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

As the concentration of the reactant increases, effective collision between the reactant molecules also increases. And thus, the reaction rate also increases. It is the main principle of the collision theory.

Option  A is the correct answer.

Multiple choice chemistry how far? how fast? collision theory collision theory of chemical reactions rate of chemical reaction

An increase in the rate of a reaction for a rise in temperature is due to:

  1. increase in collision frequency

  2. shortening of mean free path

  3. increase in the number of activated molecules

  4. none of the above
Reveal answer Fill a bubble to check yourself
A,B,C Correct answer
Explanation

An increase in the rate of a reaction for a rise in temperature is due to  increase in collision frequency, shortening of mean free path and increase in the number of activated molecules.
Increasing the temperature increases reaction rates because of the disproportionately large increase in the number of high energy collisions. It is only these collisions (possessing at least the activation energy for the reaction) which result in a reaction.

Multiple choice chemistry how far? how fast? collision theory collision theory of chemical reactions rate of chemical reaction

Effective collisions are those in which molecules must:

  1. have energy equal to or greater than the threshold energy

  2. have proper orientation

  3. acquire the energy of activation

  4. all of the above
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Option (D) is correct. These are the characteristics of effective collisions.
Effective collisions are collision between two reactants with the appropriate orientation & with sufficient energy to overcome the activation energy barrier.
The number of effective collisions increases exponentially with an increase in temperature.

Multiple choice chemistry how far? how fast? collision theory collision theory of chemical reactions rate of chemical reaction

The rate of a chemical reaction generally increases rapidly even for small temperature increase because of a rapid increase in:

  1. Collision frequency

  2. Fraction of molecules with energies in excess of the activation energy

  3. Activation energy

  4. Average kinetic energy of molecules
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Every chemical reaction whether exothermic or endothermic has an energy barrier which has to be overcome before reactants can be transformed into products. If the reactant molecules have sufficient energy, they can reach the peak of the energy barrier after collision and then they can go to the right side of the slope and consequently change into products. If the activation energy for a reaction is low, the fraction of effective collisions will be large and the reaction will be fast. On the other hand, if the activation energy is high, then fraction of effective collisions will be small and the reaction will be slow. When temperature is increased, the number of active molecules increases, i.e., the number of effective collisions will increase and the rate of reaction will increase.

Multiple choice chemistry how far? how fast? collision theory collision theory of chemical reactions rate of chemical reaction
Which statements describe the condition(s) required for a successful formation of a product in a reaction ?

  1. The collision must involve a sufficient amount of energy, provided from the motion of the particles, to overcome the activation energy

  2. The relative orientation of the particles has little or no effect on the formation of the product

  3. The relative orientation of the particles has an effect only if the kinetic energy of the particles is below some minimum value

  4. The relative orientation of the particles must allow for formation of the new bonds in the product

  5. The energy of the incoming particles must be above a certain minimum value and the relative orientation of the particles must allow for formation of new bonds in the product
Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

The statement (E) describe the conditions required for a successful formation of a product in a reaction.
The energy of the incoming particles must be above a certain minimum value (called activation energy) and the relative orientation of the particles must allow for formation of new bonds in the product.

Multiple choice chemistry how far? how fast? collision theory collision theory of chemical reactions rate of chemical reaction

Two molecules collide and a reaction not occur. Which of the following is not a valid explanation for this?

  1. The molecules were not in the proper states of matter.

  2. The molecules did not have enough kinetic energy.

  3. The molecules were not oriented correctly when they struck each other.

  4. The temperature of the reaction mixture was not high enough.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

For a reaction to occur,

$(i)$ The two molecules must collide with proper orientation.

$(ii)$ They should have high kinetic energy.

$(iii)$ The temperature should be high.

$(iv)$ But the state of matter does not have any effect on the reaction.

The states of matter molecules do not affect the rate of reaction.

Multiple choice chemistry how far? how fast? collision theory collision theory of chemical reactions rate of chemical reaction

What are effective collisions?

  1. Collisions leading to the transformation of reactants to products

  2. formation of activated complex

  3. collison between two reactant to decrease the activation energy

  4. collison between two reactant to overcome activation energy barrier
Reveal answer Fill a bubble to check yourself
B,D Correct answer
Explanation

 The effective collisions are collisions leading to the transformation of reactants to products.
This will happen when (i) the reactant species collide (ii) the colliding molecules have total kinetic energy equal to or greater than the activation energy of the reaction (iii) the colliding molecules must have proper orientation relative to each other.

Multiple choice chemistry how far? how fast? collision theory collision theory of chemical reactions rate of chemical reaction

For a chemical reaction to occur, all of the following must happen except.

  1. A large enough number of collisions must occur

  2. Chemical bonds in the reactants must break

  3. Reactant particles must collide which enough energy for change to occur

  4. Reactant particles must collide with correct orientation
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
For a chemical reaction to occur, bonds must break in reactant so that new bonds are formed. Moreover, reactants must collide with energy greater than activation energy for change to ocur.
Also, reactant must have proper orientation for reaction.
However, it is not necessary that enough number of collisions must occur.
Multiple choice chemistry how far? how fast? collision theory collision theory of chemical reactions rate of chemical reaction

According to the collision theory, most molecular collisions do not lead to a reaction. Which of the following is(are) necessary for collisions to successfully lead to the reaction?

  1. The total kinetic energy of the collision must be greater than some minimum value.

  2. A catalyst must be present at the collision.

  3. The colliding particles must be properly oriented in space when they collide.

  4. None of the above.
Reveal answer Fill a bubble to check yourself
A,C Correct answer
Explanation

The conditions (A) and (C) are necessary for the collisions to successfully lead to reaction .
For an effective collision, molecules must possess sufficient energy (called activation orientation) and proper orientation. The presence of catalyst is not essential for collision as reaction can occur even in absence of a catalyst.