topic 6

Collision theory

* Proper orientation


* Collision


* Sufficient energy to overcome repulsive forces and break the bonds (activation energy)

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What is the cause behind unsuccessful collisions?

Particles don’t have sufficient energy

Define activation energy

Minimum energy required for colliding particles to react

Rate of dissociaciation

* negative
* change in concentration of reactants / change in time
* mol dm-3 s-1

Rate of formation

* positive
* change in product concentration/ change in time
* mol dm-3 s-1

When can you use a colorimeter to measure rate?

If the solution changes color

How to measure rate of reaction for gas in an open system?

Change in mass/Change in time

How can volume be used to measure rate?

* gas syringe, inverted measuring cylinder
* Gas production is measure in a closed system
* Change in volume/Change in time

Exothermic reactions

* Reactants are higher than products
* Higher Ea than endothermic reactions

Endo thermic reactions

* Products are higher than reactants

Where is transition state on a graph and what does it indicate?

* Highest energy peak
* Simultaneous breaking and forming of bonds

Where is the activation energy on a graph?

The distance between reactants and the transition state

What is the effect of a catalyst on activation energy?

* provide an alternative reaction pathway with lower Ea
* increases frequency of proper collision

What is the effect of increasing concentration on reactions?

* more particles in set volume = higher collision frequency, higher rate

What is the effect of increasing pressure on reactions?

* gases
* less space = increased collision frequency = higher rate

What is the effect of increasing temperature on reactions?

* higher velocity = higher frequency of collisions = higher rate
* higher proportion with Ea = higher proportion of successful collisions = higher rate

What is the effect of size on rate of reaction?

* smaller size = higher SA = more particles able to collide = higher frequency of successful collisions = higher rate
* solids

What does Maxwell-Boltzmann curve show?

distribution of kinetic energy at a certain temperature

Effect of increasing temperature on Maxwell-Boltzmann curve

* Curve flattens
* peak shifts to the right
* right line goes over the original curve
* higher proportion of molecules at or beyond Ea

Effect of catalyst on Maxwewll-Boltzmann curve

* curve doesn’t shift
* line indicating molecules with Ea shifts to the left