Thermodynamics II Flashcards
Give an example of a spontanous exothermic reaction
Dissolving 1 mole of CuSO4 in 250cm3 water will give a temperature rise of 70°C
Are all spontaneous reactions endothermic
No
e.g. ice melts at room temperature
Give an example of a spontaneous endothermic reaction
NH4NO3 -> NH4(+)(aq) + NO3(-)(aq) where delta H= +28.05kJmol-1
Are ice crystals ordered or disordered in arrangment
Ice crystals are highly ordered
Are liquid water molecules ordered or disordered in arrangement
Liquid water is fairly ordered
Are water vapour molecules ordered or disordered in arrangment
Water vapour and steam are random in arrangement and so disordered
What is the second law of thermodynamics
During spontaneous change, energy and matter become more disordered
In the second law of thermodynamics what does energy refer to
The release of enthalpy (exothermic reaction)
In the second law of thermodynamics what does matter refer to
An increase in entropy
What does the fact that not all spontaneous reactions are endothermic mean
That energy and matter are not equally important and one dominates in a spontaneous reaction
What is the Gibbs Free Energy equation
ΔG = ΔH - TΔS
What does ΔH refer to in the Gibbs free energy equation
Enthaply change
What does ΔS refer to in the Gibbs free energy equation
Entropy change
What does T refer to in the Gibbs free energy equation and what unit does this value possess
Temperature in K (+273 to °C)
What does it mean if ΔG
The reaction is spontaneous if ΔG is a negative value
What does it mean if ΔG > 0
The reaction is not spontaneous if ΔG is a positive value
According to Gibbs free energy how can a reaction still be spontaneous if ΔH is positive (endothermic)
If a reaction is endothermic the reaction can still be spontaneous if the ΔS value is large enough that a negative ΔG value is still produced
What value is ΔG is a reversible reaction once the reaction has reached equlibrium
ΔG = 0 and the reaction seems to stop
In regards to reversible reactions what reactions occur at equlibirum
There is a mixture of the forwards and backwards reactions which are occurring at a constant rate resulting in a mixture of the products of the two reactions being present and the reaction appears to have stopped
What is the equation of a reversible reaction at equilibrium
aA + bB cC + dD
Once a reversible reaction is at equilibrium what equation can you use to find the equilibrium constant
K= (C^c x D^d/ A^a x B^b)equilibrium
If K is a big value what does this mean
The concentration of products is higher and the concentration of reactants is lower
If K is a small value what does this mean
The concentration of products is lower and the concentration of reactants is higher
Why do you have to wait until a reaction has reached equilibrium until you calculate the equilibrium constant
The composition of the substance no longer changes once the reaction has reached equilibrium
