thermodynamics and kinetics Flashcards
kinetics
rate of reaction depends on the pathway from reactants to products
thermodynamics
tells us whether a reaction is spontaneous based only on the properties of reactants and products
exergonic reaction
ΔG< 0
reaction is spontaneous
endergonic reaction
ΔG> 0
the reaction is not spontaneous
endergonic reaction in biochemistry
they will be coupled with exergonic reactions that will give them the energy to occur
1st law of thermodynamics
ΔE = q + w
ΔE = change in internal energy
q= heat transferred
w= work done
the internal energy of a system
U= potential + kinetic energye
exothermic reaction
there is a reduction of the potential energy: the new bonds formed have less potential energy than the ones of the reactants. New bonds that are formed are stronger than one of the reactants
enthalpy of a reaction
change in the
potential energy
what happens in spontaneous processes
we have an increase of disorder
entropy
a thermodynamic function that increases with the number of energetically equivalent ways to arrange the components of a system
the greatest number of microstates
highest entropy
2nd law of thermodynamics
the total entropy of an isolated system can never decrease over time.
Gibbs free energy
G= ΔH - TΔS
positive ΔG
reaction is non-spontaneous
negative ΔG
reaction is spontaneous
rate equation
rate = change in concentration of reactants or products/ time
factors that affect the rate of a reaction
- nature of the reactants
- conc of the reactants
- temperature
- presence of catalysts
why can Ca react more vigorously than Mg
this is bc the ionisation energy decreases down in the group so the reactivity increases as you go down
reaction rate equation
V = k [A]a [B]b [C]γ
k: reaction constant-> temp dependent
v: reaction rate
not a, b, γ not stoichiometric coefficients
rate-determining step
slowest step
2-step mechanism
1st step has a higher activation energy than the second step. so the 1st step is much slower than the 2nd step and so the 1st step determines the overall rate of reaction
activation energy
energy that must be provided to compounds to result in a chemical reaction. it is energy that is required to reach the activated complex
how do we get from the reactant to the product
the molecule must go through a high-energy state called the activated complex/ transition state
arrhenius equation:
k= Ae ^-Ea/RT
A= frequency factor
Ea= activation energy
Boltzmann maxwell distribution
the higher the temp, the wider the energy distribution and the greater the average energy. The proportion of molecules that have an energy equal to or greater than the Ea is greater and therefore they are more likely to react
catalysts
a substance that increases the rate of a chemical reaction but is not consumed by a reaction. catalysts work by providing an alternative pathway for the reaction one in which the RDS has a lower Ea
effect of catalysts on the position of the equilibrium
does not affect it
