CHEMISTRY AND ENERGYHow are they related?

What is Energy?

Defined as the ability to do work or create heat.

Many types of energy Thermal Light Gravitational Kinetic Potential

Light Energy

The Dual Nature of Light (or electrons IN light):    1.Sometimes it behaves like a particle (called a photon), which explains how light travels in straight lines    2.  Sometimes it behaves like a wave, which explains how light bends (or diffracts) around an object     3.  Scientists accept the evidence that supports this dual nature of light

Light is a form of energy called electromagnetic energy a. Other types of electromagnetic energy include

radio, microwave , heat (infrared), ultraviolet (UV) and many other types

Electromagnetic energy travels in waves The waves are different from each other in their

lengths – called wavelength         a.  Wavelength is the distance between 2 waves         b.  The crest is the highest point of a wave         c.  The trough is the lowest point of a wave         d.  The amplitude is how high the wave is        e.  Frequency is the number of waves in a given period of time

Electromagnetic Spectrum

The shorter the wavelength and the greater the frequency, the higher the energy         a.  Radio waves are as long as soccer fields, low frequency and low energy         b.  Gamma rays are smaller than an atom, high frequency and high energy

Electromagnetic Spectrum Continued

What Does This Energy Look Like?

How Are They All Related

Frequency, wavelength and the speed of light are related by the following equation:

c = λν where c is the speed of light 3.00 x 108

m/s ν is the frequency measured in Hz

(hertz) (s-1) λ is the wavelength measured in nm

(nanometers)

Lets Look at an Example

What is the frequency of a photon with λ = 550 nm

Light Energy and Bohr’s Model

the Bohr model depicts an atom as a small, positively charged nucleus surrounded by electrons. These electrons travel in circular orbits around the nucleus—similar in structure to the solar system, except electrostatic forces rather than gravity provide attraction.

Properties of Bohr’s Model

Electrons in atoms orbit the nucleus. Electrons can only orbit stably in

certain orbits ("stationary orbits“- remember the ladder rungs ).

These orbits are associated with definite energies and are also called energy shells or energy levels. REMEMBER THAT ALL ELECTRONS IN THE SAME ORBITAL ON THE SAME ENERGY LEVEL ARE DEGENERATE.

So How Can Electrons Move?

Electrons can only gain or lose energy by jumping from one orbit to another

To go from a lower energy to a higher energy, electromagnetic radiation is absorbed

To go from a higher energy to a lower energy electromagnetic radiation is emitted in the form of photons (little packets of light)

Electron Energy Calculations ΔE = hν ΔE = hν ΔE = hν

1) E is the energy of the particular quantum of energy under study measured in Joules (J)

2) h stands for a fundamental constant of nature now known as Planck's Constant. The value for Planck's

Constant is 6.626 x 10¯34 Joule second (Js).

3) ν is the frequency of the particular photon being studied (still measured in s-1)

Lets Look at a Problem

Remember the problem from a few slides ago? Now lets calculate the energy in a wavelength of that frequency

Thermochemistry

The study of heat used or released in a chemical reaction.

Specific Heat Calculations q = mCΔT

q = heat (J or cal or Cal)4.184 cal = 1 Joule1000 cal = 1 Cal (dietary

calorie)m = mass (g)C = specific heat (J/g oC or cal/g

oC)ΔT = change in temperature (o C

or K) = Tf - Ti

Specific Heat

Specific heat of water = 4.184 cal /g o C or

= 1 J / goC

Specific heat of most metals = < 1 J / goC

Do metals heat slowly or quickly compared to water?

Do metals stay warm longer or shorter than water?

Practice Problem

How much energy is required to heat 120.0 g of water from 2.0 oC to 24.0oC?

q = mCΔTm= 120.0 gC = 4.184 J/goCΔT= (24.0 – 2.0)oC = 22.0oC

q = (120.0g)(4.184 J/goC)(22.0oC) =

Practice Problem

How much heat (in kJ) is given off when 85.0 g of lead cools from 200.0oC to 10.0 oC? (Specific heat of lead = 0.129 J/g oC)

q = mCΔTm = 85.0 gC = 0.129 J/g oCΔT = (10.0 – 200.0)oC = -

190.0oCq = (85.0 g)(0.129 J/g oC)(- 190.0oC) =

-

How Do Chemical Reactions Create Heat energy? Consider the combustion of gasoline

(octane)2 C8H18 +25 O2 16 CO2 +18

H2O Potential Energy: Stored energy

Potential energy is stored in the bonds of the reactant s and the products

When bonds are broken, the energy is available

When product bonds form, some energy is used in the formation of these bonds

The excess energy is released as heat

Kinetic Energy

Directly related to temperature

Is Heat Used or Released?

Endothermic reactions use heat from the surroundings Sweating Refrigeration

Exothermic reactions releases heat to the surroundings Hot hands Combustion Exercise

Endothermic Reactions

Decrease in kinetic energy decrease in temperature heat will transfer from the environment to the system resulting in a cooler environment

Absorbs heat from its surrounding. The system gains heat Positive value for q H = q = 0 Hproducts Hreactants

Exothermic Reactions

Increase in kinetic energy increase in temperature of system heat released to the environment resulting in a hotter environment

Releases heat to its surroundings The system loses heat Negative value for q H = q = 0 Hproducts Hreactants

Enthalpy

Heat content for systems at constant pressure

Symbol is H Terms heat and enthalpy are used

interchangeably for this course H = q = m C T

Heat moves from ________ to ___________.

Law of Conservation of Energy

Energy is not lost or gained in a chemical reaction

 In a chemical reaction potential energy is transferred to kinetic energy

Thermochemical Equations

An equation that includes the heat change

Example: write the thermochemical equation for this reaction CaO(s) + H2O(l) Ca(OH)2(s) H = -

65.2 kJ

CaO(s) + H2O(l) Ca(OH)2(s) + 65.2 kJ

Stoichiometry and Thermochemistry

Tin metal can be extracted from its oxide according to the following reaction:

SnO2(s) + 4NO2(g) + 2H2O(l) + 192 kJ Sn(s) + 4HNO3(aq)

How much energy will be required to extract 59.5 grams of tin?

How to solve

1. Use your stoichiometry2. Treat heat as a reactant or

productSnO2(s) + 4NO2(g) + 2H2O(l) +

192 kJ Sn(s) + 4HNO3(aq)

59.5 g Sn 1 mol Sn 192 kJ

1 g Sn 1 mol Sn

If an Object feels hot, it means it is undergoing a change with a H that is:

a. positiveb. negativec. whether the object feels hot

or not is unrelated to its Hd. I don’t know  

If the object feels hot, it means it is undergoing:

a. an exothermic reactionb. an endothermic reactionc. whether it feels hot or not is

unrelated to whether it is undergoing an exothermic or an endothermic change

HEAT DURING A CHANGE OF STATE

How does ice melt?

What Is a Phase Change?

Is a change from one state of matter (solid, liquid, gas) to another.

Phase changes are physical changes because:

- It only affects physical appearance, not

chemical make-up.

- Reversible

What Happens During a Phase Change

During a phase change, heat energy is either absorbed or released.

Heat energy is released as molecules slow down and move closer together.

Heat energy is absorbed as molecules speed up and expand.

What Happens During a Phase Change

Melting and Boiling Points Melting Point: The temperature

at which a solid changes into a liquid.

Boiling Point: The temperature at which a liquid changes into a gas.

What is a Freezing point? Compare the freezing and melting points of water.

Molar Heat of Fusion (or Melting) Heat absorbed by one mole of a

substance during melting Constant temperature Hfus

H2O(s) H2O(l) H = 6.01 kJ/mol

Molar Heat of Solidification (or Freezing) Heat lost when 1 mole of a liquid

solidifies Temperature is constant Hsolid

Hfus = -Hsolid

H2O(l) H2O(s) H = -6.01 kJ/mol

Molar Heat of Vaporization (or Boiling) Heat needed to vaporize 1 mole

of a liquid Hvap

H2O(l) H2O(g) Hvap = 40.7 kJ/mol

Molar Heat of Condensation Heat released when 1 mole of

vapor condenses Hcond

H2O(g) H2O(l) Hcond = -40.7 kJ/mol

Hvap = -Hcond

Heating Curve for Water

What Determines Phase

Whether a substance is a solid, liquid or gas depends on the temperature and pressure

Keeping T constant while increasing P usually produces a solid

Water is an exception, increasing pressure on ice produces water This causes ice skates to melt ice

and freezing water to expand and produce frost heaves

Before We Look at a Phase Diagram…

Phase Diagram Plot of Pressure versus

Temperature Triple Point

A point on the phase diagram at which all three phases exist (solid, liquid and gas)

Critical Point A point on the phase diagram at

which the density of the liquid and vapor phases are the same

Phase Diagram

Phase Diagram Features

Beyond the critical point there is no distinction between a liquid and gas

Solid and liquid phases separated by a fusion curve

Solid and gas phases separated by a sublimation curve

In Conclusion