reaction rates and equilibrium

How does pressure effect rate of reaction?

only in gases

-higher pressure increases rate, more particles in the same volume, more frequent collisions

how does concentration effect rate of reaction?

-increased conc. increases reaction rate, more particles in same volume, more frequent collisions BETWEEN REACTANT PARTICLES

-graph levels off earlier

how does temperature effect rate of reaction?

-increased temperature increases rate

-reactant particles gain kinetic energy, move around faster, collide more frequently

-more particles exceed activation energy, more successful collisions

What's the role of a catalyst?

increases rate of chemical reaction

offers alternative pathway

with a lower activation energy

so more molecules exceed activation energy

remains unchanged

What are homogenous and heterogenous catalysts

-homogenous is in same phase/state as reactants

Whats the benefit of using catalyst (iron) in terms of economical importance in haber process

-less energy needed, reduces energy costs

-carried out at 200 instead of 400 atmospheres as there's a safety risk of explosions and it's uneconomical

-carried out at 450 degrees C, reduces equilibrium yield as forward reaction exothermic but increases rate or reaction

compromise between chemical equilibrium and reaction rate

Whats the boltzmann ditribution

-peak is most probably energy

-mean energy of molecules is greater than most probably energy

-area under curve = number of particles

-graph doesn't touch x-axis at the end as there's no maximum energy that a particle can have

how does temperature/catalyst effect boltzmann distributuion

-as temperature increases, peak lowers and shifts to the right as more particles exceed activation energy

-GREATER AREA UNDER CURVE ABOVE Ea

-catalyst just lowers Ea

What's dynamic equilibrium?

in closed system

rate of forward reaction = rate of reverse reaction

concentrations of reactants and products remain constant

both reactions still take place

whats le chataliers principle

when a chemical system is at equilibrium and a change is made to some of its conditions, the system responds to oppose these changes

Does the catalyst effect the equilibrium position?

no, only increases rate of BOTH reactions

what's the equilibrium law

Kc (equilibrium constant)

bigger number means position of equilibria lies more on the right

ONLY AFFECTED BY TEMPERATURE, NOT PRESSURE

Describe how rate of reaction changes as time goes on

-rate is highest at the start, highest conc. of reactant particles, most frequent collisions

-rate decreases as products form and conc. of reactants decreases, less frequent collisions between reactant particles

-reactant stops when all of one reactant is used up (limiting reactant)

activation energy definition

the minimum amount of energy needed to start a chemical reaction by breaking bonds in reactant molecules

How does a catalyst work?

-reaction takes place on surface of catalyst

reactant molecules form weak temporary bonds with surface of catalyst at the expense of their existing bonds getting weaker

- 2 molecules collide on surface of catalyst, bonds break more easily

how does increasing pressure effect position of equilibrium in haber process (N2 + 3H2 = 2NH3)

system acts to decrease pressure

forward reaction favoured as less gas molecules on the right

position of equilibrium shifts to right

equilibrium yield of ammonia increases

how does increasing temperature effect position of equilibrium in haber process (forward reaction exothermic)

system acts to decrease temperature

reverse reaction favoured as it's endothermic

position of equilibrium shifts to the left

equilibrium yield of ammonia decreases

RATE of ammonia forming INCREASES

What happens to rate of reaction if you use a weaker acid?

-decrease

-less H+ ions solution PARTIALLY DISSOCIATES

-less reactant particles

-less frequent collisions

How does surface area affect the rate of reaction?

it increases the rate of reaction because increasing the surface area of solid reactants increases the frequency of collisions

What happens if the concentration of an acid is halved in a reaction?

-half the volume of product is made

Why is the use of catalysts in industrial processes important for the environment?

-can carry out reaction at lower temperatures

-lower energy demand

-less burning/combustion of fossil fuels

-less CO2 made

why are some reactions exothermic

more energy is released in forming bonds than is absorbed to break bonds

quantities to monitor rate of reaction

concentration decrease, mass decrease, volume increase