Chemistry SM-1131Week 4 Lesson 1

Dr. Jesse ReichAssistant Professor of Chemistry

Massachusetts Maritime AcademyFall 2008

Class Today• Poem• Wiki- projects• Understanding a chemical reaction• Matter and changes of Matter: physical v. chemical

properties, physical changes v. chemical changes• Separating Matter• Energy and Temperature, maybe some problems• Atomic Theory: ie your wiki by D. Reich

The New ColossusNot like the brazen giant of Greek fame,With conquering limbs astride from land to land;Here at our sea-washed, sunset gates shall standA mighty woman with a torch, whose flameIs the imprisoned lightning, and her nameMother of Exiles. From her beacon-handGlows world-wide welcome; her mild eyes commandThe air-bridged harbor that twin cities frame."Keep, ancient lands, your storied pomp!" cries sheWith silent lips. "Give me your tired, your poor,Your huddled masses yearning to breathe free,The wretched refuse of your teeming shore.Send these, the homeless, tempest-tost to me,I lift my lamp beside the golden door!”

Emma Lazarus, 1883

Friday- No Class for Real

• I’ll give you another take home quiz on Wednesday that I want you to complete.

Chemical Reaction

• When matter undergoes a composition change we call it a chemical reaction.

• We write them like this:

Reactants ProductsReactants are the substances before the change.Products are what are formed after the reaction.

Properties

• Properties: The characteristics we use to distinguish one substance from another.

• Chemical vs. Physical properties

Physical Properties

• Is it this? Is it that? Does it look like this? Does it feel like that?

Chemical Properties

• What happens when it does? When it interacts with _____ what happens? Did it change from ____ to ____ when we made it?

Evidence of Chemical RXNs

• Odor• Color Changes• Heat and Light• Sound• Bubbling• Explosions

Separating Mixtures

• Decanting: pour off liquid leaving solids• Distillation: evaporate off a material that boils

more quickly (Volatile) than the one it’s mixed with.

• Filtration: Solids are separated from a liquid by pouring both through a porous material.

Conservation of Mass and Energy

• There is a chemical law:Mass and Energy is neither created nor

destroyed in a chemical reaction.

Energy = “The capacity to do work”

Energy Types

• Kinetic, Potential, Electrical, Chemical

Units

• Joule: the SI equivalent of a calorie, 1 cal = 4.184 J

• calorie (cal) the amount of energy required to raise the temperature of 1g of water 1 degree C.

• Calorie (Cal) = 1000 cals• Kilowatt-hour (kWh) = 3.6e6 j

You should practice converting units

• 23 Cal into cal• 45 joules into Cal• 3 kWh to cal

Energy during changes

• Chemists tend to think of compounds having potential energy. If they have a lot of stored energy we normally think they are high energy. If they are un-reactive we consider them low energy.

Endothermic and Exothermic

Endothermic Exothermic

Requires Energy Releases Energy

Temperature• How much thermal energy something has.• K = C + 273• C = (F -32) 1.80C = Freezing Water 100C = boiling water32F = freezing water 212F= boiling water 96F body

temp0K means there is no thermal energy at all. There is no

lower temperature possible than 0K.

Heat Capacity

• The amount of energy needed to change the temperature of a given amount of it 1C.

• When the mass of the compound is expressed in grams then the term is “specific heat capacity” or “specific heat”

• Water has a high heat capacity. So it takes a lot of energy to make it hot. Boiling water takes a long time. Showering uses a lot of energy.

Calculating Heat Capacity

• Heat = Mass x Specific Heat Capacity x Temp Change q = m x C x T

T = Tfinal - Tinitial

This is a 4 variable problem. How many values do you have to know to find one of them?

Can you solve for m? C? or TIf q is positive it means the temperature goes upIf q is negative it means the Temp went down.

Democritus

The material cause of all things that exist is the coming together of atoms and void. Atoms are too small to be perceived by the senses. They are eternal and have many different shapes, and they can cluster together to create things that are perceivable. Differences in shape, arrangement, and position of atoms produce different things. By aggregation they provide bulky objects that we can perceive with our sight and other senses.

We see changes in things because of the rearrangement of atoms, but atoms themselves are eternal. Words such as ‘nothing’, ‘the void’, and ‘the infinite’ describe space. Individual atoms are describable as ‘not nothing’, ‘being’, and ‘the compact’. There is no void in atoms, so they cannot be divided. I hold the same view as Leucippus regarding atoms and space: atoms are always in motion in space.

(www.humanistictexts.org)

~460, Greece-371 BCE

His Buddy Aristotle

• Aristotle emphasized that nature consisted of four elements: air, earth, fire, and water.

The Greek GodsEmpedocles associates the Elements with four Gods: Hera (Earth), Persephone (Water), Zeus (Air) and Hades (Fire),

Fast Forward to Dalton

Sept. 6, 1766, England-July 27, 1844

 Dalton's Atomic Theory

1) All matter is made of atoms. Atoms are indivisible and indestructible.2) All atoms of a given element are identical in mass and properties3) Compounds are formed by a combination of two or more different kinds of atoms.4) A chemical reaction is a rearrangement of atoms.

Dalton’s Creek, err, element set

Dalton’s Laws• “I see no sufficient reason why we may not conclude

that all [gases] under the same pressure expand equally by heat and that for any given expansion of mercury, the corresponding expansion of air is proportionally something less, the higher the temperature” 1801

• “I am nearly persuaded that the circumstance depends on the weight and number of the ultimate particles of the several gases." 1805

So what changed?

abyss.uoregon.edu

Crooks Tube

Current moved from the cathode to the anode through a vacuum

It moved in lines similar to light

But magnets could deflect the current

The new path could be used to calculate a mass to charge ratio but couldn’t calculate mass or charge

J. J. ThompsonDec. 18, 1856, England - Aug. 30, 1940

Wilhelm Conrad Röntgen

March 27, 1845, Germany - Feb. 10, 1923 “On the evening of November 8, 1895, he found that, if the discharge tube is enclosed in a sealed, thick black carton to exclude all light, and if he worked in a dark room, a paper plate covered on one side with barium platinocyanide placed in the path of the rays became fluorescent even when it was as far as two metres from the discharge tube. During subsequent experiments he found that objects of different thicknesses interposed in the path of the rays showed variable transparency to them when recorded on a photographic plate. When he immobilised for some moments the hand of his wife in the path of the rays over a photographic plate, he observed after development of the plate an image of his wife's hand which showed the shadows thrown by the bones of her hand and that of a ring she was wearing, surrounded by the penumbra of the flesh, which was more permeable to the rays and therefore threw a fainter shadow. This was the first "röntgenogram" ever taken. In further experiments, Röntgen showed that the new rays are produced by the impact of cathode rays on a material object. Because their nature was then unknown, he gave them the name X-rays. Later, Max von Laue and his pupils showed that they are of the same electromagnetic nature as light, but differ from it only in the higher frequency of their vibration.” (nobelprize.org)

Henri BecquerelDec. 15, 1952, France – Aug. 25, 1908

Following a discussion with Henri Poincaré on the radiation which had recently been discovered by Röntgen (X-rays) and which was accompanied by a type of phosphorescence in the vacuum tube, Becquerel decided to investigate whether there was any connection between X-rays and naturally occurring phosphorescence. He had inherited from his father a supply of uranium salts, which phosphoresce on exposure to light. When the salts were placed near to a photographic plate covered with opaque paper, the plate was discovered to be fogged. The phenomenon was found to be common to all the uranium salts studied and was concluded to be a property of the uranium atom. Later, Becquerel showed that the rays emitted by uranium, which for a long time were named after their discoverer, caused gases to ionize and that they differed from X-rays in that they could be deflected by electric or magnetic fields. For his discovery of spontaneous radioactivity Becquerel was awarded half of the Nobel Prize for Physics in 1903, the other half being given to Pierre and Marie Curie for their study of the Becquerel radiation. (nobelprize.org)

Check Your Sock DrawerFurther investigation, on the 26th and 27th of February, was delayed because the skies over Paris were overcast and the uranium-covered plates Becquerel intended to expose to the sun were returned to a drawer. On the first of March, he developed the photographic plates expecting only faint images to appear. To his surprise, the images were clear and strong. This meant that the uranium emitted radiation without an external source of energy such as the sun. Becquerel had discovered radioactivity, the spontaneous emission of radiation by a material. He himself stated to the French Academy of Sciences "There is an emission of rays without apparent cause. The sun has been excluded" (epswww.unm.edu)

A Nobel Next to Socks

Pause for Dramatic EffectWhat We Know Up to Now!

• There are different elements• Elements are made up of atoms• Atoms have positive and negative components• Some elements are radioactive

Anyone for a Curie

November 7, 1867, France – July 4, 1934She helped to discover Polonium and Radium. To do this she and her husband took Pitchblend, which contained the radioactive element Uranium by the ton and carefully isolated the radioactive components over several years. What they found was that there were more than one radioactive element in it because they found an element that was far more radioactive than the element uranium.

She got a Nobel in Physics for radioactivity.She got a Nobel in chemistry for discovering two new elements.

A Wonderful Place to WorkWith her Husband

Raw Materials

Pitchblende Radium

There is 1 gram of radium in 7 tons of pitchblende

“It therefore appeared probable that if pitchblende, chalcolite, and autunite possess so great a degree of activity, these substances contain a small quantity of a strongly radioactive body, differing from uranium and thorium and the simple bodies actually known. I thought that if this were indeed the case, I might hope to extract this substance from the ore by the ordinary methods of chemical analysis.” [Curie 1961 (1903), p. 16].

How Did She Do It?

In her own wordsIf we assume that radium contains a supply of energy which it gives out little by little, we are led to believe that this body does not remain unchanged, as it appears to, but that it undergoes an extremely slow change. Several reasons speak in favor of this view. First, the emission of heat, which makes it seem probable that a chemical reaction is taking place in the radium. But this is no ordinary chemical reaction, affecting the combination of atoms in the molecule. No chemical reaction can explain the emission of heat due to radium. Furthermore, radioactivity is a property of the atom of radium; if, then, it is due to a transformation, this transformation must take place in the atom itself. Consequently, from this point of view, the atom of radium would be in a process of evolution, and we should be forced to abandon the theory of the invariability of atoms, which is the foundation of modern chemistry [M. Curie 1904].

Ernest RutherfordAug. 30, 1871 New Zealand – Oct. 19, 1937

In Simpler terms…

So what just happened?It was almost as incredible as if you fired a 15-inch

shell at a piece of tissue paper, and it came back to hit you

"On consideration, I realized that this scattering backwards must be the result of a single collision, and when I made calculations I saw that it was impossible to get anything of that order of magnitude unless you took a system in which the greater part of the mass of the atom was concentrated in a minute nucleus. It was then that I had the idea of an atom with a minute massive center carrying a charge."

WTH?

So what’s an atom look like?

The Planetary Model

Robert A. MillikanMarch 22, 1868, U.S.A. – Dec. 19 1953

•Established the charge of an electron and •Determined the atomic structure of electricity

So What’d He Do?

Well, what’s that thingy?

www.physchem.co.za

So, what’d it look like inside?

www.nikhef.nl

So, what changed?

A Nagging Concern

Rutherford’s Model

Positive Protons and Oppositely Charged ElectronsWhat should happen?Collapse!