Equilibrium

• what is a reversible reaction ?

  reactions that take place both in the forward and backward direction
• what is dynamic equillibrium ?

  the rate of the forward reaction is equal to the rate of the reverse reaction

  the concentration of reactants and products do not change
• why does the concentration of reactants and products remain unchanged in a equilibrium system ?

  as fast as the reactants are becoming products , the products are reacting to become reactants and so the rate of reaction for both reactions are the SAME
• for a reaction to be in equillibrium does the system have to be closed or open ?

  closed
• what is a closed system ?

  its isolated from its surroundings so the temp, pressure and concentration of reactants and products are unaffected by outside influences
• what does the position of equillibrium mean ?

  where the reaction is shifted to and making more of ( the extent of the reaction )
• what does le chateliers principle state ?

  when a system in equilibrium is subjected to an external change the system readjusts itself to minimise the effect of that change
• so if equilibrium has been disrupted by adding more molecules

  the position of equilibrium shifts to minimise the change
• what is the effect of concentration on equillibrium ?

  changing the concentration of a reactant or product in an equilibrium system will change the rate of the forward or reverse reaction

  so if more products are formed equilibrium shifts to the right

  if there are more reactants formed the equilibrium has been shifted to the right

  to make more of them thats why its been shifted
• what is an investigation that could be done to show effects of concentration ?

  a reaction between chromate ions and dichromate ions

  changes colour from yellow to orange
• what are the changes you would see ?

  if you added an acid to the chromate ions this increases the reaction of the h plus ions and so this increases the conc of the reactanst equilibrium will shift to the right to make more products to minimise the effect of the increased reactants concentration and so the solution turns orange due to the position of equilibrium shifting to the right
• what happens if i had a hydroxide ?

  when sodium hydroxide was added this reacts with the h plus ions and so it decreases the concentration of the reacts and so equllibrium shifts to the left to make more reactants to minimise the effect of the change from the the hydroxide and so the solutions turns yello
• what is the effect of temperature on equilibrium ?

  an increase in temp shifts the equilibrium position in the endothermic direction where enthalpy change is positive

  a decrease in temp shifts the equilibrium position to the exothermic directions where enthalpy change is negative
• whats an investigation for the effects of temperature on equilibrium ?

  cobalt chloride when dissolves in water forms a pink solution

  1. dissolve coblat chloried in a boiling quanity of HCL and then place this in boiling water which forms a pink colour
  2. then set up a boiling water bath and transfer the the boiling tube into boiling water which causes the solution to turn a blue colour
  3. transfer the boiling tube into ice water and it turns to pink colour
• what are the changes you will see ?

  in the boiling water due to the increase in temperature equilibrium shifts to minimise the change by shifting to the right in the endothermic side to minimise the increase in temp by absorbing the heat so the solution turns a blue colour

  in the ice tube due to the decrease in temp the equilibrium shifts to the left to the exothermic side to release more heat
• when writing a answer what do u always say first

  whether the forward reaction is endothermic or exothermic
• so if the temp increases and the forward reaction is exothermic

  position of equillibrium shifts to the left to make more reactants
• so if the temp increases and the forward reaction is endothermic

  the position of equilibrium shifts to the right to make more products
• so if the temp decreases and the forward reaction is exothermic

  the position of equilibrium shifts to the right to make more products
• so if the temp decreases and the forward reaction is endothermic

  the position of equilibrium shifts to the left to make more reactants
• what is the effect of pressure on equilibrium ?

  the change only occurs if one side has more moles of gas then the other side

  if there is the same moles on both sides no changes occur
• how do we investigate pressure on equilibrium

  nirogen dioxide and dinitrogen teroxide have different colours brown and colourless

  the pressure of the gas is proportional to the conc of the container nitrogen dioxide has 2 moles and dinitrogen teroxide has one mol
• what are the changes we see if we increase the pressure

  the position of equllibrium will shift to the side with fewer moleucles to reudce the pressure and so since there are fewer molecule son the right , position of equlibrium shifts to the right to make more products to minimise the effect of the increased pressure so the brown fades and more colourless gas is formed
• when given a question on pressure what do you state first

  which side there are more moles of gas on
• what is the effect of a catalyst on equilibrium ?

  it doesnt change the position of equilibrium as it speeds up the rate of the forward and the backwards at the same rate HOWEVER

  it will increase the rate at which equilibrium is established
• what is the equilibrium constant ?

  the actual position of equilibrium
• what does the magnitude of the equilibrium constant mean ?

  if there are more reactants or more products in an equilibrium system
• whats the formula for Kc

  [C]c [D]d

  ---------

  [A]a[B]b

  
  

  products/reactats
• what are square brackets for ?

  concentration of
• what does the little c mean ?

  raising the number to the number before the compound (the balancing number )
• if the Kc value is 1 what does that mean ?

  the position of equilibrium is halfway between reactants and products
• if the Kc value is more then 1 what does that mean ?

  the position of equilibrium is shifted towards the products
• if the Kc value is less then 1 what does that mean ?

  position of equilibrium is shifted towards the reactants
• if the Kc value is high what does this mean ?

  the further the position of equilibrium to the right and the greater the conc of the products compared to reactants
• what does homogeneous equilibria mean ?

  Equilibrium reached when all reactants and products are in the same phase.
• what does heterogeneous equilibria mean ?

  equilibrium species that have different states or phases
• if we have a heterogeneous equlibira what do we ignore ?

  solids and liquids and only focus on gasses and aqueous if ITS hetro if its homo and all of the species are liquids then we have to take into account all of them
• how do we do an ice table ?

  step 1: We must always first calculate equilibrium amounts(moles) of all reactants and products from the given experimental data using ICE table

  Step 2: Calculate the equilibrium concentrations in moldm-3

  Step 3: Plug these equilibrium concentration values in your Kc expression. Write your answer to correct significant numbers. Also, work out units for Kc.