Tag: rate of chemical reaction

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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

A chemical reaction occurs as a result of collisions between reacting molecules. Therefore, the reaction rate is given by:

  1. total number of collision occuring in a unit volume per second

  2. fraction of molecules which possess energy less than the threshold energy

  3. total number of effective collisions

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

According to collision theory, the reaction occurs when molecules collide with each other. The rate is given by:

Rate=${ Z } _{ AB }\times f$

Where $Z _{AB}$=collision frequency of reactants $A$ & $B$.

i.e. total number of collisions occurring in a unit volume per second. &

$f$=fraction of effective collisions.

So, the rate depends on both (A) & (C)

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

Unit of frequency factor (A) is:

  1. mol/L

  2. mol/L.s

  3. depend upon order of reaction

  4. it does not have any unit
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The Arrhenius equation is k = A * e^(-Ea/RT). The units of the frequency factor A must match the units of the rate constant k, which depend on the order of the reaction (e.g., s^-1 for first order, M^-1 s^-1 for second order).

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

How an increase in concentration is related to number of collisions?

  1. Directly

  2. Inversely

  3. Has no effect

  4. None
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The increase in concentration is directly related to number of collisions.
For higher concentrations, the average distance between molecules is small. Due to this, the number of collisions increases.
For lower concentrations, the average distance between molecules is large. Due to this, the number of collisions decreases.

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

Assertion: Reactions happen faster at higher temperatures.
Reason: As temperatures increase, there is also an increase in the number of collisions with the required activation energy for a reaction to occur.

  1. Both Assertion and Reason are true and Reason is the correct explanation of Assertion

  2. Both Assertion and Reason are true but Reason is not the correct explanation of Assertion

  3. Assertion is true but Reason is false

  4. Assertion is false but Reason is true

  5. Both Assertion and Reason are false
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

When you raise the temperature of a system, the molecules bounce around a lot more. They have more energy. When they bounce around more, they are more likely to collide. 

That fact means they are also more likely to combine. When you lower the temperature, the molecules are slower and collide less.

Reason is the correct explanation for assertion.

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.