Dynamic Equilibrium

what is a reversible reaction

a reaction where the reactants react to form the products, AND the products can react to form the reactants again.

what is the arrow used in an equation for a reversible reaction

what is a closed system

none of the reactants / products can escape and no matter can enter

how is equilibrium established

as reactants react, concentration of reactants falls, so the forward reaction slows
as more and more products are produced and their concentrations rise, the backward reaction speeds up.
eventually the forward and backward reactions are still happening, but at exactly the same rate
therefore the concentrations of the products and reactants remain constant

what does the graph of a reversible reaction look like

an overview of Le Chatelier’s principle

the position of equilibrium and the yield of products / reactants can be altered by changing the conditions of the reversible reaction. these conditions can include:

• Pressure (if all substances are gases)

• Temperature

• Concentration of products/ reactants

• Removing products / reactants

how does increasing the concentration of reactants affect equilibrium
how does increasing the concentration of products affect equilibrium

reactants:

• more products can be produced, so equilibrium moves to the right to the lower concentration side

products:

• more reactants can be produced so equilibrium moves to the left to the lower concentration side

how does removing a product affect equilibrium

equilibrium moves to the right. if product continues to keep being removed, equilibrium continues to move rightwards. this turns this into a one-way reaction.

how does an increase in pressure affect equilibrium
how does a decrease in pressure affect equilibrium

increase:

• equilibrium moves to the side with fewer moles to counteract the higher pressure. the side with the fewer moles increases in yield

decrease:

• equilibrium moves to the side with more moles to counteract the lower pressure. the side with the more moles increases in yield

what effect does equilibrium have if the numbers of moles on each side are the same OR not all substances are gases

the position of equilibrium does not change

what effect does increasing temp on a reversible reaction have
what effect does decreasing temp on a reversible reaction have
assume forward reaction is exothermic, and backward reaction is endothermic

increase:

• equilibrium must shift to reduce temp. it must absorb heat you just put in

• therefore more of the reverse, endothermic reaction occurs to absorb the heat

• equilibrium moves to left as more reactants are produced

decrease:

• equilibrium must shift to raise temp. must release heat

• therefore more of forward, exothermic reaction occurs to absorb the heat

• equilibrium moves to right as more products are produced

what is ammonia used in the UK (4)

fertilisers, dyes, explosives, medicine

the equation of the haber process

nitrogen + hydrogen —> ammonia
N2 + 3H2 —> 2NH3

where does the nitrogen and hydrogen come from in the haber process

nitrogen comes from the air, and hydrogen comes from natural gas - mainly methane

what conditions are used for haber process and how are costs reduced

• medium pressure of 200 atm (atmospheres)

• temperature of around 450C

• iron catalyst used to speed up reaction

costs reduced by recycling unreacted hydrogen and nitrogen

why is a temperature of 450C used in the haber process

• forward reaction is exothermic, so yield of ammonia is greater at lower temps

• but lower temps make rate of reaction really slow

• so high temp used to make ammonia faster, even though yield is lower

why is a medium pressure of 200 atm used in the haber process

• reactants (nitrogen and hydrogen) have more molecules (4) than the products (ammonia, 2) so a higher pressure makes a larger yield of ammonia - and it increases rate of reaction, so a large yield is made fast

• but high pressure requires stronger, more expensive pipes and is dangerous

• so medium pressure of 200 atm used