Tag: how far? how fast?

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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.

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

What does it mean when a collision is elastic?

  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.
Reveal answer Fill a bubble to check yourself
A Correct answer
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

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

Among the following which will decrease the rate of the reaction?
i. Using highly concentrated reactants
ii. Decreasing the temperature by $25\ K$
iii. Stirring the reactants

  1. i only

  2. ii only

  3. i and iii only

  4. ii and iii only

  5. i, ii, and iii
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$\bullet $  Using highly concentrated reactants will increase the rate of the reaction as rate is directly proportional to the 

    concentration of reactants.
$\bullet $  Decreasing the temperature by 25 K will decrease the rate constant and hence the rate of reaction will decrease.
$\bullet $  Stirring the reactants increases the rate of interaction between the reactants and hence the rate of reaction increases.
$\therefore $ The correct answer is (ii) only.

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

_________ increases 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
  5. $\displaystyle pH$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

An increase in the reactant concentration increase effective collisions without increasing average energy.

This is due to the fact that molecules comes more and more closer, hence, they tends to collide more easily.

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

In a reaction carried out at 400 k, $0.0001\%$ of the total number of collisions are effective. The energy of activation of the reaction is:

  1. zero

  2. 7.37 k cal/mol

  3. 9.212 k cal/mol

  4. 11.05 k cal/mol
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

We know that, Arrhenius equation for calculation of energy of activation of reaction with rate constant $K$ and temeperature $T$ is 

$K=A$ $e^{-Ea/RT}$
where, $Ea$= Arrhenius activation energy
$A$= pre exponential factor (frequency factor)

Now, $e^{-Ea/K _BT}$= Fraction of collision having more than activation energy
where, $K _B=$ Boltzmann constant
Given, $T=400$ $K$       and effective collision= $0.0001$%

$\Rightarrow$ Effective Collision= $e^{-Ea/K _BT}$
$\Rightarrow$ $0.0001$%= $e^{-Ea/1.3\times 10^{-23}\times 400}$
$\Rightarrow$ $10^{-6}$= $e^{-Ea/1.3\times 10^{-23}\times 400}$

$\Rightarrow$ $2.303\times \log 10^{-6}$= $\cfrac {-Ea}{1.3\times 10^{-23}\times 400}$
$\Rightarrow$ $2.303\times (-6)$= $\cfrac {-Ea}{1.3\times 10^{-23}\times 400}$

$\Rightarrow$ $Ea$= $1.3\times 10^{-23}\times 400\times6\times 2.303=7.19\times 10^{-20}$ $J/mol$