Chemistry SM-1131Week 3 Lesson 2

Dr. Jesse ReichAssistant Professor of Chemistry

Massachusetts Maritime AcademyFall 2008

Class Today

• Friday• Wiki• Matter- physical v. chemical, physical changes

v. chemical changes• Separating Matter• Wednesday = Energy and Temperature, maybe

some problems

Friday

• I misspoke. We do have class on Friday, but I’m going to “cancel” it.

• Class on Friday is meant to be spent working on your Wikis. Get at least one scientist on your wiki!

Density

• Density = Mass volume

d = m v

Let’s calculate density

• I have a ball of metal that takes up 3ml and weighs 12.6g. What is it’s density?

d = m v

d= 12.6g= 4.2 g/ml, but 3ml only has 1 sig fig 3mlOK so, finally 4 g/ml would be the answer!

Matter

• Definitions: vocab. words to memorize• Matter: Anything that has mass and takes up

space.• Elements: The most basic different types of

matter. You can’t break it down into other substances.

• Atoms: The smallest distinguishable unit of an element.

• Molecules: 2+ more atoms bonded together.

Solid, Liquid, Gas

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Elements, Compounds, Mixtures

• If there is only 1 atom type or molecule type in a given space we call it a pure substance

• If there are 2 or more atom types or molecules in a given space we call it a mixture.

Mixture

• When you combine at least two pure elements, at least two pure compounds, or at least 1 pure element and 1 pure compound into the same space.

Homogeneous Mixture

Heterogeneous Mixture

New Material

• Chemical v Physical• Energy

Properties

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

• Chemical vs. Physical properties

Physical Properties

• Physical Properties don’t change what it’s made up of.

• Temperature changes, physical location, color, appearance, melting point, boiling point, density, cutting it into smaller pieces, smushing, location changes.

• If you change phase solid-> liquid it’s still the same compound. So its physical.

Chemical Properties

• A chemical property is displayed when its composition is changed.

• Can it be burned? Is it corrosive? Is it acidic? Toxic?

• When something burns it turns into different chemicals.

• When something rusts the chemical composition changes!

Chemical Reaction

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

• We write them like this:Reactants Products

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

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

• There is a chemical law:Mass is neither created nor destroyed in a

chemical reaction.

Energy

• “The capacity to do work”• Energy is conserved: ie it is neither created

nor destoryed

Kinetic Energy

• Energy in motion

Potential Energy

• Stored energy that could “potentially” be released

Electrical Energy

• Energy associated with the flow of electrons.

Chemical Energy

• Energy stored when compounds are formed and released when compounds react.

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.

Homework

• Copy the example problems 3.10 and 3.11 from the book

• Make sure you HW answers use sig figs and scientific notation

• You will get this one chance and only this one chance to fix your HW from chapter 1&2 and turn it in for credit.

Homework

• Get your wiki up. Put in a couple of scientists• Get your homework in by Monday

Extra Time

• Heat = Mass x Specific Heat Capacity x Temp Change

q = m x C x T• What amount of heat is needed to 250g of

water from 55C to 85C if the heat capacity of water is 4.18J

gC• q = 250g x 4.18J x 30C =31350J = 3.1e4 J gC