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

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

  1. $0.25Z$
  2. $2Z$
  3. $0.50Z$
  4. $Z$
Reveal answer Fill a bubble to check yourself
D Correct answer
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.

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

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?

  1. X/N

  2. NX
  3. $2NX$
  4. $NX/2$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The collision frequency Z is related to the number of collisions per unit volume. For a gas with N molecules per unit volume, the collision frequency is given by Z = (sqrt(2) * pi * d^2 * v_avg * N^2) / 2. The standard expression for collision frequency per unit volume is proportional to N^2, but given the options and the definition of X, the factor of 1/2 accounts for double counting in binary collisions.

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

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

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

The number of collisions with the walls per unit time is proportional to the average speed of the molecules. Since average speed is proportional to the square root of temperature, increasing the temperature increases the collision frequency.

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

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

  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
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

When 1.0g of H2 gas is heated in a closed flask, its temperature increases, which raises the pressure, the rate of molecular collisions, and the kinetic energy of the gas molecules. However, because the flask is closed, the total amount of gas remains constant, meaning the number of moles of gas does not change. Therefore, the statement that the number of moles increases is incorrect.

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

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

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

Helium (molar mass 4) has a higher average speed than Neon (molar mass 20) at the same temperature. Because collision frequency with walls is proportional to average speed, Helium molecules strike the walls more frequently.

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

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

  1. Collision number increases

  2. Collision frequency increases

  3. Mean free path increases

  4. Number of molecules per unit volume increases
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

When temperature increases at constant pressure, the volume must increase (Charles's Law). The number of molecules per unit volume (N/V) decreases. The collision number (collisions per molecule) is related to the frequency of collisions, which depends on density and speed.

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)