Tag: chemistry

Questions Related to chemistry

Collision frequency of a gas at $1\ atm$ pressure is $Z$. Its value at $0.5\ atm$ will be:

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

  1. $0.25Z$

  2. $2Z$

  3. $0.50Z$

  4. $Z$

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Correct Option: D
Explanation:

$\rightarrow$ As the pressure increases collision frequency increases.

$\rightarrow$ Vice versa pressure is decreased to half, frequency of collision decreases to half.
Hence option $C$ is correct.

If X is the total number of collisions which a gas molecule registers with other molecules per unit time under particular conditions, then the collision frequency of the gas containing N molecules per unit volume is?

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

  1. X/N

  2. NX

  3. $2NX$

  4. $NX/2$

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Correct Option: D

The number of collisions of Ar atoms with the walls of container per unit time?

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

  1. Increases when the temperature increases

  2. Remains the same when $CO _2$ is added to the container at constant temperature

  3. Increases when $CO _2$ is added to the container at constant temperature

  4. Decreases, when the average kinetic energy per molecule is decreased

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Correct Option: A

In a closed flask of $5$l $1.0$g $H _2$ is heated from $300$ to $600$K. Which statement is not correct?

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

  1. Pressure of the gas increases

  2. The rate of collisions increases

  3. The number of moles of gas increases

  4. The energy of gas molecules increases

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Correct Option: A

One mole of helium and one mole of neon are taken in a vessel. Which of the following statements are correct?

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

  1. Molecules of helium strike the wall of vessel more frequently

  2. Moles of neon apply more average force per collision on the wall of vessel

  3. Molecules of helium have greater average molecular speed

  4. Helium exerts higher pressure than neon

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Correct Option: A

When the temperature of an ideal gas is increased at constant pressure?

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

  1. Collision number increases

  2. Collision frequency increases

  3. Mean free path increases

  4. Number of molecules per unit volume increases

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Correct Option: A

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

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

  1. increase in collision frequency

  2. shortening of mean free path

  3. increase in the number of activated molecules

  4. none of the above

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Correct Option: A,B,C
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.

Effective collisions are those in which molecules must:

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

  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

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Correct Option: D
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.

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

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

  1. Collision frequency

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

  3. Activation energy

  4. Average kinetic energy of molecules

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Correct Option: B
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.

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

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

  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

Show answer
Correct Option: A,C
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)