Collision theory - class-XII

In elastic collision of identical balls, velocities are exchanged. A(0.5) gives 0.3 to B, B(-0.3) gives -0.5 to A. Final: A=-0.3 m/s, B=0.5 m/s. Mass cancels out.

Increasing the temperature of the substance, increases the fraction of molecules which collide with energies greater than $Ea$. For every $10^0 C$ rise in temperature, the fraction of molecules having energy equal to or greater than Ea gets doubled leading to doubling the rate of reaction.

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. 

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.

Collision diameter will be least for the low molecular weight.

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

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.

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.

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.

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.

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.

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.

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.

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)

The Arrhenius equation is k = A * e^(-Ea/RT). The units of the frequency factor A must match the units of the rate constant k, which depend on the order of the reaction (e.g., s^-1 for first order, M^-1 s^-1 for second order).

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.

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. 

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.

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.

 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 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.

(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

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

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

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