Module 2 thingz

Question 1

What is Enthalpy?

Answer 1

The enthalpy is the heat of a reaction measured under conditions of constant pressure

Question 2

How do we find DeltaRH?

Answer 2

Combining the DeltaRH values for the chemical equations.

Question 3

What is Standard Enthalpy of Formation?

Answer 3

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

Question 4

What is entropy?

Answer 4

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

Question 5

What is a spontaneous reaction?

Answer 5

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

Question 6

What are the characteristics of a reaction which is spontaneous at all temperatures?

Answer 6

• -> Negative H
• -> Positive S
• -> Negative G

Question 7

What are the characteristics of a reaction which is non-spontaneous at all temperatures?

Answer 7

• -> Positive H
• -> Negative S
• -> Positive G

Question 8

What are the characteristics of a reaction which is Spon at low T and non spon at high T?

Answer 8

• -> Negative H
• -> Negative S
• -> Positive or negative G

Question 9

What are the characteristics of a reaction which is spon at high T and non spon at low T?

Answer 9

• -> Positive H
• -> Positive S
• -> Positive or negative G

Question 10

What are the spontaneity characteristics of ionic solids?

Answer 10

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

Question 11

What is Gibbs energy?

Answer 11

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

Question 12

What is a coupled reaction?

Answer 12

If a reaction is non spec, then coupling it to a spon one may give an overal reaction with a negative value for gibbs.

Question 13

What are the units of rate?

Answer 13

mol L-1 s-1

Question 14

What is rate affected by?

Answer 14

1. Chemical nature
2. Physical states of the reactants and products
3. Concentrations of the reactants
4. Temperature
5. Presence of a catalyst or an inhibitor

Question 15

What is zero rate laws unit?

Answer 15

mol L-1 s-1

Question 16

What is 2nd rate law units?

Answer 16

s-1

Question 17

What is 3rd rate law units?

Answer 17

mol-1 L s-1

Question 18

What is a pseudo first order reaction?

Answer 18

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.

Question 19

What is the integrated rate law graph?

Answer 19

Y axis = In[A]t
X axis = t
Intercept = In[A]o
Slope = -k

Question 20

What are reaction intermediates?

Answer 20

Species which play a role in the conversion of reactants to products but do not appear in the overall chemical equation.

Question 21

What is a reaction mechanism?

Answer 21

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.

Question 22

What do you do if there are intermediates in the rate law?

Answer 22

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.

Question 23

What is Molecularity?

Answer 23

The Molecularity defines the number of molecules that must collide
for the reaction to occur.

Question 24

What is Arrhenius equation?

Answer 24

Combines both the collision rate and the collion effectiveness
k = Ae-Ea/RT

Question 25

What is the A in Arrhenius Equation?

Answer 25

A is called the frequency factor and is related to the probability of the reactant molecules
colliding in the correct orientation.

Question 26

What is the plotting for the Arrhenius equation?

Answer 26

Intercept: InA
Slope: -Ea/R
Y = InK
X = 1/T

Question 27

How do you assign reduction/oxidation in galvanic cells?

Answer 27

If the value of Ecell is positive, reduction is occurring on the right hand side

If the value of Ecell is negative, oxidation is ocurring on the right hand side

Question 28

What is the exeption to standard conditions?

Answer 28

All species at 1 mol exept for H+ which is at 1x10-7 (at pH = 7)

Question 29

What are biological catalysts?

Answer 29

Coenzymes. They enable electron transfer, but react very slowly without a catalyst

Question 30

What is a transition metal complex?

Answer 30

Consists of some number of ligands bonded to a transition metal cation. The bond is covalent, in which both the electrons come from the ligand . The ligand is a lewis base and the metal cation is a lewis acid

Question 31

What are water ligands?

Answer 31

The most abundant ligand. In most cases octahedral complex ions are formed.

Question 32

How can the ligand influence a transition metal?

Answer 32

Modifies the reduction potential of the transition metal ion. If the ligand can pull electron density away from the metal ion, it will have a greater desire for and electron, therefore its reduction potential will be increased.

• -> Electronegative ligands increase E potential e.g. Fluorine
• -> Non electronegative ligands decrease E potential e.g. CH3