Tag: chemistry

Questions Related to chemistry

Unit of frequency factor (A) is:

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

  1. mol/L

  2. mol/L.s

  3. depend upon order of reaction

  4. it does not have any unit

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Correct Option: C

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

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

  1. Directly

  2. Inversely

  3. Has no effect

  4. None

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Correct Option: A
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.

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.

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

  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

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Correct Option: A
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.

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

Show answer
Correct Option: E
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.

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

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

  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.

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Correct Option: A
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.

What are effective collisions?

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

  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

Show answer
Correct Option: B,D
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.

The fraction of collisions that posses the energy $E _a$ is given by:

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

  1. $f = e^{\frac{-Ea}{RT}}$

  2. $f = e^{\frac{Ea}{RT}}$

  3. $f = e^{- Ea.RT}$

  4. $f = e^{Ea.RT}$

Show answer
Correct Option: A
Explanation:
$k=Pze^{\cfrac {-Ea}{RT}}$
$\cfrac kA$ or $\cfrac k{Pz}= $ Fraction of collision possessing $E _a$
$\therefore$ Fraction of collision possessing energy $E _a= \cfrac kA$
$=\cfrac {Ae^{-E _a/RT}}{A}$
$f=e^{-E _a/RT}$

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

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

  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

Show answer
Correct Option: A
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.

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?

chemistry how far? how fast? collision theory collision theory of chemical reactions rate of chemical 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.

Show answer
Correct Option: A,C
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.

What does it mean when a collision is elastic?

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

  1. No energy is gained or lost.

  2. Energy is gained.

  3. Energy is lost.

  4. The particles can stretch out.

  5. The particles slow down.

Show answer
Correct Option: A
Explanation:

(A) , No energy is gained or lost.
An elastic collision is an encounter between two bodies in which the total kinetic energy of the two bodies after the encounter is equal to their total kinetic energy before the encounter. Elastic collisions occur only if there is no net conversion of kinetic energy into other forms