Chemical Kinetics

Unit 2

What makes a collision successful?

Particles collide with enough energy (Activation energy) and with the right geometry (orientation).

What are the four factors that affect reaction rates?

Concentration of reactants, Temperature of system, Surface area of solid reactants, Catalysts.

How does the concentration of reactants affect reaction rates?

The greater the concentration the more reactant particles there are to collide, increasing the frequency of collisions. more collisions means more successful collisions means faster reaction rate.

What are the two ways the temperature of a system affect reaction rates?

The higher the temperature the higher the kinetic energy which makes the reactant particles move faster, increasing collision frequency. Faster, higher energy particles make for higher energy collisions, so more collisions will be high enough energy to react.

How does the surface area of solid reactants affect reaction rate?

Greater surface area means more frequent collisions, increasing reaction rate.

What are catalysts and how do they affect reaction rate?

A substance added to a reaction to change the reaction mechanism to one with a lower activation energy. Catalysts will not be used up in a reaction.

What is a transition state of activated complex?

The continuous process of breaking old bonds and forming new ones started by a successful collision between reactant particles.

What is activation energy?

The energy needed to form a transition state

What is a reaction mechanism?

The sequence of steps that take place in a chemical reaction.

What is an elementary reaction?

A reaction that happens in a single step.

Why won’t a reaction involving more than three reactant particles be elementary?

The probability of 4+ reactant particles colliding with enough energy and correct geometry is too low.

Will the rate determining step have the largest or the smallest activation energy?

Largest.

What does molecularity refer to?

The number of reactant particles in a step of a reaction.

What are the three terms that describe molecularity?

Unimolecular, Bimolecular, Termolecular.

What is Ea?

Activation energy.

What is enthalpy change (Delta H)?

The heat of the reaction.

If Delta H is negative, is the reaction exothermic or endothermic?

Exothermic.

If Delta H is positive, is the reaction exothermic or endothermic?

Endothermic.

What is the equation for the differential rate law?

Rate = k [E1]^m [E2]^n

What is k in the differential rate law equation?

The rate constant, dependant on temperature.

What are m and n in the differential rate law equation?

The overall order of the reaction.