CHEM 120: Introduction to Inorganic Chemistry

Instructor: Upali Siriwardane (Ph.D., Ohio State University)

CTH 311, Tele: 257-4941, e-mail: upali@chem.latech.edu

Office hours: 10:00 to 12:00 Tu & Th ; 8:00-9:00 and 11:00-12:00 M,W,& F

Chapters Covered and Test dates

Tests will be given in regular class periods from 9:30-10:45 a.m. on the following days:

September 22,     2004 (Test 1): Chapters 1 & 2

October 8,           2004(Test 2): Chapters 3, & 4

October 22,         2004 (Test 3): Chapter 5 & 6

November 12,     2004 (Test 4): Chapter 7 & 8

November 15   Brief survey of chpater 9-10

November 17,      2004 MAKE-UP: Comprehensive test (Covers all chapters 1-8)

Grading:

[( Test 1 + Test 2 + Test3 + Test4 + Test5)] x.70 + [ Homework + quiz average] x 0.30 = Final Average

                                            5

Chapter 8. Chemical and Physical Change: Energy, Rate, and Equilibrium

Thermodynamics

1. Endothermic and exothermic based on heat flow between a system and its surroundings.

2. Enthalpy (DH), entropy (DS) , and free energy (DG)

3. Experiments to get thermochemical information and fuel values.

Reaction Rates

4. Reaction rate and the role of kinetics in chemical and physical change.

5. Activation energy and the activated complex and effects on reaction rate.

6. Predict the affect of, concentration, temperature, and catalysis on the rate of a chemical reaction.

7. Write rate equations for elementary processes.

Chemical Equilibrium

8. Equilibrium chemical reactions.

9. Equilibrium-constant expressions and equilibrium constants.

10.LeChatelier's principle for predicting equilibrium position.

Thermodynamics

Thermodynamics is study of energy, heat and work.

As chemists we are interested in heat changes in chemical and physical changes.

Aim: to predict whether a change (both physical and chemical ) will occur spontaneously when left to itself--do we have to do anything other than mix the reactants together to make it occur?

Chemical reaction and energy

In a chemical reaction heat is released or absorbed by our system to or from the surroundings. In a chemical reaction convert energy in bonds into heat energy (and vice versa).

We can measure the energy changes in these processes.

Universe

System:

Surroundings:

Universe:

First law of thermodynamics

Law of Conservation of Energy:

Thermochemistry

Heat changes during chemical reactions

Thermochemical equation. eg.

H₂ (g) + O₂ (g) ---> 2H₂O(l) DH =- 256 kJ;

DH is called the enthalpy of reaction.

if DH is + reaction is called endothermic

if DH is - reaction is called exothermic

Exothermic processes

In an exothermic process

Exothermic rxn

Reactants

DE

products

Endothermic Reaction

In an endothermic reaction

Endothermic process

                                          products

                                                                 DE

       reactants

Enthalpy, H

Define enthalpy (H):

Normally talk about a change in enthalpy (DH, DH^o):

Enthalpy, H

If DH is negative

Slide 15

Enthalpy, H

If DH is positive

Slide 17

Are these exo- or endothermic?

When solid NaOH is dissolved in water the soln gets hotter.

S(s) + O₂(g) g SO₂(g) DH^o = -71kcal

N₂(g) + 2O₂(g +16.2kcal g 2NO₂(g)

Spontaneous Processes

A spontaneous reactions is one that occurs without us having to do anything to it (once it has started). (No external energy input)

Name some spontaneous processes.

Note that one direction is spontaneous, the reverse is not.

"We want to come up..."

We want to come up with a way of predicting whether something will be spontaneous.

It has been observed that many exothermic processes are spontaneous.

Question: Does exothermicity guarantee that something is spontaneous?

"Look at H₂O(s)"

Look at H₂O(s) g H₂O(l) DH^o_rxn=1.44kcal

Entropy, S

Entropy (S, S^o) is a measure of the disorder, or randomness of a system.

The greater

Entropy info

"For a rxn:"

For a rxn: DS_rxn= sum of entropy of all the products minus the sum of the entropy of all the reactants.

Get entropy increases

When go from a system of

Is there an entropy increase when

A log burns in a fireplace

Water vapor condenses on a cold surface

A solid metal melts

Water boils

Does a positive entropy change insure a spontaneous process

Look at H₂O(l) g H₂O(s)

DS<0 but

Second law of thermodynamics

The entropy of the universe increases in a spontaneous process and is equal to zero in a system at equilibrium.

Not always easy to calculate the entropy change of the universe.

Define a new quantity, G, Gibbs free energy. G refers to the system we are studying.

"DG = DH -..."

DG = DH - T DS

This equation combines the exothermicity and positive entropy criteria.

Criterion for spontaneity

If DG < 0

If DG > 0

If DG = 0

How does DG = DH - T DS
work?

Look at H₂O(l) g H₂O(g) water boiling

DH= 10.6kcal and DS =0.0284kcal

DG = DH -T DS

at 50^oC DG =

at 100^oC DG =

at 120^oC DG =

DG = DH - T DS

An exothermic rxn that has a positive entropy change is

An endothermic rxn that has a negative entropy change is

DG = DH - T DS

An exothermic rxn that has a negative entropy change is spontaneous

An endothermic rxn that has a positive entropy change is spontaneous

Calorimetry: how to measure heat changes in reactions

Measure heat change (temp inc or dec) in a quantity of water or solution that is in contact with the reaction of interest and is isolated from the surroundings.

Slide 34

To calculate the amt of heat (Q) absorbed or released

Q= m x SH x DT

Q = heat change; DT = temperature change = T_final-T_initial

Add heat, temp inc; remove heat temp dec

Specific heat (SH) = the amount of heat (cal) required to raise the temperature of one g of a substance by 1°C

"Units of SH : cal..."

Units of SH : cal/(g ^oC); [SH of H₂O= 1.00 cal/(g ^oC); of Al = 0.21 cal/(g ^oC)]

Calc the amt of heat liberated (in cal and kcal) from 366 g of aluminum when it cools from 77.0^oC to 12.0^oC.

10kJ of heat is supplied to 1000g of H₂O and to 1000g of Al. Calc the inc in temp for both.

"To raise the temp of..."

To raise the temp of a mass of water from 25^oC to 50^oC requires 7.5 kcal. What is the mass of the water?

A sample of Al weighs 67 g. If 854 cal of heat are required to raise the temp of this sample from 25^oC to 85^oC, calculate the specific heat of aluminum.

Fuel value

Fuel value is amt of energy per gram of food.

One nutritional Calorie (C) = 1 kcal = 1000 cal; 1 cal = 4.184 J; 1 kcal=1 Cal =4.184 kJ

8.7: A 1.00 g sample of a candy bar (which contains a lot of sugar was burned in a bomb calorimeter. A 3.0^oC temp increase was observed for 1.00 x 10³g of water. The entire candy bar weighed 2.5 ounces. Calc the fuel value (in nutritional Calories) of the sample and the total caloric content of the candy bar.

"8.8:"

8.8: If the fuel value of 1.00g of a certain carbohydrate is 3.00 nutritional Calories, how many grams of water must be present in the calorimeter to record a 5.00^oC change in temp?

Kinetics (Reaction Rates)

Thermodynamics tells us whether a reaction should occur spontaneously, but does not tell us how fast the reaction will occur. Kinetics tells us

For example, thermodynamics says that diamond will spontaneously change into graphite.

Kinetics tells us

"Look at H₂(g)"

Look at H₂(g) + I₂(g) g 2HI(g)

Let’s envision how the rreaction might occur on a molecular basis.

To react

1. H₂ must collide with I₂

2. There must be enough energy to break a H-H and a I-I bond to initiate reaction

3. The molecules must collide in the correct geometry.

"A molecule that is moving..."

A molecule that is moving has kinetic energy; faster the motion, the greater the KE. When molecules collide some of the KE is changed into vibrational energy of the bonds . Sometimes there is enough energy gained through collision to break a bond and initiate reaction. If the energy is not enough to break the bond, the molecules bounce of one another with no reaction occurring.

So there is some minimum collision energy below which no reaction occurs.

Activation energy, E_a

Slide 44

Factors that affect reaction rate

I. Structure of reacting species: A. oppositely charged species often react faster than neutral species. B. bond strength can influence rxn rate (E_a) C. size and shape of molecule can be important

"II."

II. Concentration of reactants: if increase the conc of the reactants:

"III."

III. Increase the temperature:

"IV."

IV. Physical state of reactants: reactions in solution (liquids) are often very fast. In the solid state molecules have limited motion, in the gas phase have large distances between molecules and not many collisions so these reactions may be slower. In the liquid phase the molecules (ions) are able to move and are close to each other.

"V."

V. Add a catalyst. A catalyst speeds up the rate of reaction by

. The catalyst generally works by giving a different pathway (of lower energy) for the reaction to occur. A catalyst is not used up (consumed) in a reaction. The catalyst appears to be unchanged at the end.

Biological catalysts: enzymes

Slide 50

Mathematical representation of reaction rate

Object is to develop a mathematical relationship btn rate and concs of various species: know as rate equation (law)

for A +B + C g products we say the

or

"For a rate law where"

For a rate law where rate = k [A]^x[B]^y[C]^z

say

Some sample rate laws

H₂(g) + I₂(g) g 2HI(g) rate = k[H₂][I₂]

H₂(g) + I₂(g) g 2HI(g) high P, Au catalyst rate = k

2N₂O₅ g 4NO₂ + O₂ rate = k[N₂O₅]

"2NO(g)"

2NO(g) + O₂(g) g 2NO₂(g) rate = k[NO]²[O₂]

CHCl₃(g) +Cl₂(g) g CCl₄(g) + HCl(g) rate = k[CHCl₃][Cl₂]^1/2

"A reaction is found to..."

A reaction is found to be second order in A and third order in B. Write the rate equation.

The rate equation and the rate constant have to be determined experimentally.

"Write the general form of..."

Write the general form of the rate equation for:

CH₄(g) + O₂(g) g CO₂(g) + 2H₂O(g)

2NO₂(g) g 2NO(g) + O₂(g)


	Instructor: Upali Siriwardane (Ph.D., Ohio State University)
	CTH 311, Tele: 257-4941, e-mail: upali@chem.latech.edu
	Office hours: 10:00 to 12:00 Tu & Th ; 8:00-9:00 and 11:00-12:00 M,W,& F


	Tests will be given in regular class periods from 9:30-10:45 a.m. on the following days:
	September 22, 2004 (Test 1): Chapters 1 & 2
	October 8, 2004(Test 2): Chapters 3, & 4
	October 22, 2004 (Test 3): Chapter 5 & 6
	November 12, 2004 (Test 4): Chapter 7 & 8
	November 15 Brief survey of chpater 9-10
	November 17, 2004 MAKE-UP: Comprehensive test (Covers all chapters 1-8)
	Grading:
	[( Test 1 + Test 2 + Test3 + Test4 + Test5)] x.70 + [ Homework + quiz average] x 0.30 = Final Average
	5


	Thermodynamics
	1. Endothermic and exothermic based on heat flow between a system and its surroundings.
	2. Enthalpy (DH), entropy (DS) , and free energy (DG)
	3. Experiments to get thermochemical information and fuel values.
	Reaction Rates
	4. Reaction rate and the role of kinetics in chemical and physical change.
	5. Activation energy and the activated complex and effects on reaction rate.
	6. Predict the affect of, concentration, temperature, and catalysis on the rate of a chemical reaction.
	7. Write rate equations for elementary processes.
	Chemical Equilibrium
	8. Equilibrium chemical reactions.
	9. Equilibrium-constant expressions and equilibrium constants.
	10.LeChatelier's principle for predicting equilibrium position.


	Thermodynamics is study of energy, heat and work.
	As chemists we are interested in heat changes in chemical and physical changes.

	Aim: to predict whether a change (both physical and chemical ) will occur spontaneously when left to itself--do we have to do anything other than mix the reactants together to make it occur?


	In a chemical reaction heat is released or absorbed by our system to or from the surroundings. In a chemical reaction convert energy in bonds into heat energy (and vice versa).
	We can measure the energy changes in these processes.


	Heat changes during chemical reactions
	Thermochemical equation. eg.
	H₂ (g) + O₂ (g) ---> 2H₂O(l) DH =- 256 kJ;

	DH is called the enthalpy of reaction.
	if DH is + reaction is called endothermic
	if DH is - reaction is called exothermic


	Define enthalpy (H):


	Normally talk about a change in enthalpy (DH, DH^o):


	When solid NaOH is dissolved in water the soln gets hotter.
	S(s) + O₂(g) g SO₂(g) DH^o = -71kcal

	N₂(g) + 2O₂(g +16.2kcal g 2NO₂(g)


	A spontaneous reactions is one that occurs without us having to do anything to it (once it has started). (No external energy input)
	Name some spontaneous processes.
	Note that one direction is spontaneous, the reverse is not.


	We want to come up with a way of predicting whether something will be spontaneous.

	It has been observed that many exothermic processes are spontaneous.

	Question: Does exothermicity guarantee that something is spontaneous?


	Entropy (S, S^o) is a measure of the disorder, or randomness of a system.
	The greater


	For a rxn: DS_rxn= sum of entropy of all the products minus the sum of the entropy of all the reactants.


	A log burns in a fireplace
	Water vapor condenses on a cold surface
	A solid metal melts
	Water boils


	The entropy of the universe increases in a spontaneous process and is equal to zero in a system at equilibrium.
	Not always easy to calculate the entropy change of the universe.
	Define a new quantity, G, Gibbs free energy. G refers to the system we are studying.


	DG = DH - T DS
	This equation combines the exothermicity and positive entropy criteria.
	Criterion for spontaneity
	If DG < 0
	If DG > 0
	If DG = 0


	Look at H₂O(l) g H₂O(g) water boiling
	DH= 10.6kcal and DS =0.0284kcal
	DG = DH -T DS
	at 50^oC DG =
	at 100^oC DG =
	at 120^oC DG =


	An exothermic rxn that has a positive entropy change is

	An endothermic rxn that has a negative entropy change is


	An exothermic rxn that has a negative entropy change is spontaneous


	An endothermic rxn that has a positive entropy change is spontaneous


	Measure heat change (temp inc or dec) in a quantity of water or solution that is in contact with the reaction of interest and is isolated from the surroundings.


	Q= m x SH x DT
	Q = heat change; DT = temperature change = T_final-T_initial
	Add heat, temp inc; remove heat temp dec
	Specific heat (SH) = the amount of heat (cal) required to raise the temperature of one g of a substance by 1°C


	Units of SH : cal/(g ^oC); [SH of H₂O= 1.00 cal/(g ^oC); of Al = 0.21 cal/(g ^oC)]

	Calc the amt of heat liberated (in cal and kcal) from 366 g of aluminum when it cools from 77.0^oC to 12.0^oC.

	10kJ of heat is supplied to 1000g of H₂O and to 1000g of Al. Calc the inc in temp for both.


	To raise the temp of a mass of water from 25^oC to 50^oC requires 7.5 kcal. What is the mass of the water?

	A sample of Al weighs 67 g. If 854 cal of heat are required to raise the temp of this sample from 25^oC to 85^oC, calculate the specific heat of aluminum.


	Fuel value is amt of energy per gram of food.
	One nutritional Calorie (C) = 1 kcal = 1000 cal; 1 cal = 4.184 J; 1 kcal=1 Cal =4.184 kJ
	8.7: A 1.00 g sample of a candy bar (which contains a lot of sugar was burned in a bomb calorimeter. A 3.0^oC temp increase was observed for 1.00 x 10³g of water. The entire candy bar weighed 2.5 ounces. Calc the fuel value (in nutritional Calories) of the sample and the total caloric content of the candy bar.


	8.8: If the fuel value of 1.00g of a certain carbohydrate is 3.00 nutritional Calories, how many grams of water must be present in the calorimeter to record a 5.00^oC change in temp?


	Thermodynamics tells us whether a reaction should occur spontaneously, but does not tell us how fast the reaction will occur. Kinetics tells us
	For example, thermodynamics says that diamond will spontaneously change into graphite.
	Kinetics tells us


	Look at H₂(g) + I₂(g) g 2HI(g)
	Let’s envision how the rreaction might occur on a molecular basis.
	To react
	1. H₂ must collide with I₂
	2. There must be enough energy to break a H-H and a I-I bond to initiate reaction
	3. The molecules must collide in the correct geometry.


	A molecule that is moving has kinetic energy; faster the motion, the greater the KE. When molecules collide some of the KE is changed into vibrational energy of the bonds . Sometimes there is enough energy gained through collision to break a bond and initiate reaction. If the energy is not enough to break the bond, the molecules bounce of one another with no reaction occurring.
	So there is some minimum collision energy below which no reaction occurs.


	I. Structure of reacting species: A. oppositely charged species often react faster than neutral species. B. bond strength can influence rxn rate (E_a) C. size and shape of molecule can be important


	II. Concentration of reactants: if increase the conc of the reactants:


	IV. Physical state of reactants: reactions in solution (liquids) are often very fast. In the solid state molecules have limited motion, in the gas phase have large distances between molecules and not many collisions so these reactions may be slower. In the liquid phase the molecules (ions) are able to move and are close to each other.