Module 2 thingz Flashcards
What is Enthalpy?
The enthalpy is the heat of a reaction measured under conditions of constant pressure
How do we find DeltaRH?
Combining the DeltaRH values for the chemical equations.
What is Standard Enthalpy of Formation?
The Standard Enthalpy of Formation is defined as being the enthalpy change that occurs when 1 mole of
a compound is formed from its constituent elements, each in their standard states
Standard state = 0
–> Calculated using products - Reactants
What is entropy?
Entropy can be defined as a measure of the number of possible arrangements of
particles in a system. It can also refer to the number of possible energies of particles in a system.
–> Gas has more entropy then solid as it has more microstates
What is a spontaneous reaction?
A spontaneous reaction is one which, once started, will continue without any help
- -> Can be exothermic or endothermic
- -> The way to determine spontaneity is to use gibbs energy
What are the characteristics of a reaction which is spontaneous at all temperatures?
- -> Negative H
- -> Positive S
- -> Negative G
What are the characteristics of a reaction which is non-spontaneous at all temperatures?
- -> Positive H
- -> Negative S
- -> Positive G
What are the characteristics of a reaction which is Spon at low T and non spon at high T?
- -> Negative H
- -> Negative S
- -> Positive or negative G
What are the characteristics of a reaction which is spon at high T and non spon at low T?
- -> Positive H
- -> Positive S
- -> Positive or negative G
What are the spontaneity characteristics of ionic solids?
The ions have much more freedom to move around with respect to each other when in solution than they did in the lattice structure of the solid. This means that the value for ΔS is very positive for dissolution and so, in most cases, ΔG for dissolution is negative and so the process is spontaneous
What is Gibbs energy?
The change in the Gibbs Energy (ΔG) for a chemical reaction provides an indication of whether a reaction is
spontaneous in a particular direction.
–> If Gibbs is zero the reaction is in equilibrium
What is a coupled reaction?
If a reaction is non spec, then coupling it to a spon one may give an overal reaction with a negative value for gibbs.
What are the units of rate?
mol L-1 s-1
What is rate affected by?
- Chemical nature
- Physical states of the reactants and products
- Concentrations of the reactants
- Temperature
- Presence of a catalyst or an inhibitor
What is zero rate laws unit?
mol L-1 s-1
What is 2nd rate law units?
s-1
What is 3rd rate law units?
mol-1 L s-1
What is a pseudo first order reaction?
rate = k[A][B]
The reaction is dependant on the conc of the two reactants, but if B is at musch larger conc then A it will remain relatively constant so the rate law will become
rate = k[A]
It will therefore appear as a first order reaction.
What is the integrated rate law graph?
Y axis = In[A]t
X axis = t
Intercept = In[A]o
Slope = -k
What are reaction intermediates?
Species which play a role in the conversion of reactants to products but do not appear in the overall chemical equation.
What is a reaction mechanism?
The series of elementary steps is called the reaction mechanism – the sum of the elementary steps in the
reaction mechanism must be the same as the overall chemical equation.
What do you do if there are intermediates in the rate law?
Intermediates cannot be in rate laws so we rewrite the rate law, making use of the Equilibrium Constant Expression for the initial
fast equilibrium step.
What is Molecularity?
The Molecularity defines the number of molecules that must collide
for the reaction to occur.
What is Arrhenius equation?
Combines both the collision rate and the collion effectiveness
k = Ae-Ea/RT
