Module 5: Phys Chem and TMs

Question 1

Transition metal

Answer 1

A metal that the highest energy electron is in the D-sub shell and forms ions with a partially filled D-sub shell.

Question 2

what is the definition of pH?

Answer 2

pH= -log[H+]

Question 3

Define lattice enthalpy

Answer 3

The enthalpy change when I mol of a solid ionic lattice is formed from its constituent ions in gaseous states (at standard conditions)

Question 4

Write an equilibrium expression (K_c) for the following equibrium:

2A + B == 2C

Answer 4

K_c = [Products] / [Reactants]

so

K_c = [C]² / [A]²[B]

The units are M²/M³, ie M^-1. Given that M means mol dm^-3, M^-1 is mol^-1dm³.

Question 5

D-block metal

Answer 5

A metal that has its highest energy electron in the D-block sub shell.

Question 6

Define enthaply change of hydration

Answer 6

Enthaply change when one mol of a given type of gaseous ion is fully dissolved in water at standard conditions.

Question 7

Why are Zinc(Zn) and Scandium(Sc) D-block metals but not transition metals?

Answer 7

Their energy electron is in the D-block sub shell, however when they form ions they do not have a partially full D-block sub shell.

Question 8

State Le Chatelier’s Principle

Answer 8

When a change is made to a system under dynamic equilibrium, the systems responds to oppose the change.

(For example, if a reaction is exothermic going forward, increasing the temperature causes the endothermic reaction to be favoured, pushing the equilibrium towards reactants)

Question 9

What is the definition for [H⁺]?

Answer 9

[H⁺] = -10^-pH

Question 10

What is the definition of Rate of reaction?

Answer 10

rate of reaction is the change in concentration of a reactant or product per unit time.

Question 11

What is the rate constant?

Answer 11

k, is the constant that links the rate of reaction with the concentrations of the reactant raised to the powers of their orders in the rate equation.

Question 12

what does it mean by the order with respect to a reactant?

Answer 12

The order with respect to a reactant, is the the power to which the concentration of the reactant is raised in the rate equation.

Question 13

Write the rate equation for A + B -> C

Answer 13

rate= k[A]^m[B]^n

Question 14

What is the definition of the overall order?

Answer 14

overall order is the sum of all the individual orders.

Question 15

what is the calculation for rate of reaction?

Answer 15

Change in concentration of reactant or product / time

Question 16

unit of rates

Answer 16

mol dm^-3 s^-1 is the most usual, although in principle it can be change in any measurable quantity per unit time.

Question 17

Define enthalpy

Answer 17

Measure of dispersal of energy in a system

Question 18

What is the order of reaction with respect to A? If the units of Rate are moldm^-3s^-1, what are the units of k? And what effect does doubling concentration have on the rate of reaction.

Rate = k[A]⁰

Answer 18

Rate = k[A]⁰

The reaction is zero order wrt [A]

Units of k are moldm^-3s^-1

Doubling [A] has no effect on Rate

Question 19

What is the order of reaction with respect to A? If the units of Rate are moldm^-3s^-1, what are the units of k? And what effect does doubling concentration have on the rate of reaction.

Rate = k[A]²

Answer 19

Rate = k[A]²

The reaction is second order wrt [A]

Units of k are mol^-1dm³s^-1

Doubling [A] quadruples the Rate (2²=4)

Question 20

What is the order of reaction with respect to A? If the units of Rate are moldm^-3s^-1, what are the units of k? And what effect does doubling concentration have on the rate of reaction.

Rate = k[A]

Answer 20

Rate = k[A]

The reaction is first order wrt [A]

Units of k are s^-1

Doubling [A] doubles the Rate

Question 21

This graph is typical for which overall order of reaction?

Answer 21

Zeroth order

Question 22

This graph is typical for which overall order of reaction?

Answer 22

First order.

Note that half life is a constant for first order processes. The first example of this you met was radioactive decay at GCSE!

Question 23

Explain the graphs below:

Answer 23

In zeroth order reactions, increasing concentration has no effect on rate

In first order reactions, doubling the concentration will double the rate. Rate is directly proportional to concentration.

In second order reactions, doubling the concentration will quadruple the rate. Rate is proportional to concentration squared.

Question 24

Rate determining step is …

Answer 24

… the slowest step in a reaction.

The rate law (Rate = …) is based on the rate determing step.

Question 25

State the Arrhenius equation:

Answer 25

k = Aexp^-Ea/RT

R is the gas constant

T is the thermodynamic temperature

Note: A typical Ea is 40kJ mol^-1. If you subsitute this value, and temperatures of 298 and 308K, you will find that rate (or more correctly k) is approximately doubled.

The rule of thumb for any reaction is that warming by 10^oC doubles the rate.

Question 26

Describe what these graphs show as fully as possible

Answer 26

Both show starting with no products.

Over time, reactant is consumed and product forms.

Equilibrium is established when concentrations stop changing (ie, the lines are horizontal).

The left hand graph has more product than reactant (K_c>1)

The right hand graph has more reactant than product (K_c<1)

Question 27

Give examples of ligands

Answer 27

Common ligands include:

Water, :OH₂

Ammonia, :NH₃

Chloride, :Cl^-

Cyanide, :CN^-

Hydroxide, :OH^-

Question 28

What features do ligands have?

Answer 28

All ligands have a lone pair of electrons. This is used to form a dative covalent bond to a metal. Ligands might be charged, but do not have to be.

Any nucleophile can be a ligand.

Question 29

State the colour in solution and the shape of [CoCl⁴]^2-

Answer 29

[CoCl₄]^2- is a tetrahedral ion which forms a blue solution