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

What happen with the rate of the reaction when the frequency and the number of effective collisions between reacting particles increases?

  1. Increases

  2. Decreases

  3. Remains the same

  4. Approaches zero

  5. None of the above
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The atoms, ions and molecules can react to form products when they collide with enough kinetic energy and at favorable orientation. On increasing the frequency and the number of effective collisions between reacting particles increases the chance of reactants to come together to form a product  that results in the increase of rate of the reaction. 

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

What causes an increase in 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
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

As the concentration of the reactant increases, effective collision between the reactant molecules also increases. And thus, the reaction rate also increases. It is the main principle of the collision theory.

Option  A is the correct answer.

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

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.