topic 6

Collision theory

Collision theory

• Proper orientation

• Collision

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

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