1.5 reaction feasibility Flashcards
what is the feasibility of a reaction?
whether it will spontaneously take place
what is a standard enthalpy of formation? (ΔH°f)
the enthalpy change when one mole of a substance is formed from its elements in their standard state
what is the standard state of a substance?
it’s most stable state at standard conditions
what is standard conditions?
pressure of 1 atmosphere and a specified temperature, usually room temp
what is room temp?
298K, 25 degrees
what is standard enthalpy of formation for an element?
zero
where can enthalpy of formation values be found?
page 11 of the data booklet
what is a spontaneous/feasible reaction?
one which happens if it’s own accord and doesn’t need energy input
what will a feasible reaction tend towards?
the products
what is entropy (S)?
a measure of the degree of disorder
the greater the entropy, the greater the…
disorder
what level of disorder do solids have?
low
what level of disorder do gases have?
high
what entropy value does a crystal lattice at absolute zero (0K) have?
zero
what do entropy values increase with?
temperature
when does a gradual increase in entropy change to a large increase on the temperature graph?
when a change in state occurs
how does heat released by an exothermic reaction alter the entropy?
it increases it
how does heat absorbed by an endothermic reaction system alter the entropy?
it decreases it
what is the standard entropy? (ΔS)
the entropy of a substance at its standard state
where are values of standard entropy found?
page 18 of the data booklet
what does Gibbs free energy (ΔG) represent?
the excess energy available beyond what is needed to make the reaction spontaneous
what does it mean if ΔG is less than 0?
reaction is feasible/spontaneous
what does it mean if ΔG is 0?
reaction is just feasible/at equilibrium
what does it mean if ΔG is greater than 0?
reaction is not feasible/spontaneous
a reversible reaction proceeds spontaneously until…
a composition is reached where ΔG is 0
when calculating ΔG, which value must be divided by 1000?
ΔS
