Reversible Reactions and Dynamic Equilibrium Flashcards
what kind of reactions are usually deemed to be irreversible
- reactions where there is a very little (is any) amount of reactants uncombined at the end of the reaction
- where most of the maximum amount of products that could be produced are produced
what are the enthalpy changes like for these irreversible reactions
- they are very high
- being either exothermic or endothermic
what kind of reactions are deemed to be reversible reactions
- where the reactions may not go to completion
- detectable amounts of reactants remain at the end of the reaction mixed in with the products
what are the enthalpy changes for reversible reactions like
they are small
what is the condition in order for a reaction to be deemed irreversible
if the reaction is more than 99% complete
why is the reaction between HCl and NaOH said to be irreversible
- because the reaction appears to go into completion
- both reactants are almost completely ionised in water
- giving the ionic equation when they react, H+ + OH- = H2O
why could you say that that reaction isnt completely irreversible
- because pure water has a slight electrical conductivity
- meaning it can be ionised into the two original ions
- H2O = H+ + OH-
- if this water molecule is the one formed from the reaction between the reactants, this can be deemed a reversible reaction to an extent
why is this called an irreversible reaction none the less
- because only about 1 in 500 million water molecules are ionised in this way
- so we ignore this small extent of ionisation
in a reaction between hydrogen and iodine as vapors, 90% of the reactants form hydrogen iodide while the 10% dont react. the hydrogen iodide can be heated on its own to decompose it which would produce an equimolar mixture of hydrogen and iodine. what kind of reaction is this and why
- a reversible reaction
- because the products can decompose to from the original reactants as well as the volumes of them
- and only 90% of the reaction was complete, not 99%
what condition would need to be met in order for this reaction be to be in equilibrium
that there is no further change in the concentration of the reactants and products
what is the forward and backwards reaction
- the reaction between hydrogen and iodine is the forwards reaction
- the decomposition of hydrogen iodide is the backwards reaction
how is equilibrium reached in a reaction
when the rate of the forwards reaction is equal to the rate of the backwards reaction
how does the hydrogen and iodine reaction reach equilibrium
- as the hydrogen and iodine are reacting their concentrations decrease
- this causes the forward rate of reaction to decrease
- as hydrogen iodide is being formed it it begins to slowly decompose
- with increasing time as the forward reaction commences, the concentration of hydrogen iodide also increases
- leading to the rate of the backward reaction increasing
- eventually the rates of reaction become equal so there is no further change in the concentration of the reactants or products
what is the proper name for this type of equilibrium and why
- dynamic equilibrium
- because the forward and backward reaction are taking place at the same time and rate
if there was a graph for the rate of a reaction over time with lines for the forward and backward reaction, what would they look like individually
- the line for the forward reaction would start up with a high rate of reaction and fall with a gradually less steep gradient until it leveled out horizontally
- the line for the backward reaction would start the bottom (0,0) and start off with a high gradient
0 but gradually have its gradient decrease until it levels out horizontally too
