Chemistry SM-1131 Week 3 Lesson 2 Dr. Jesse Reich Assistant Professor of Chemistry Massachusetts Maritime Academy Fall 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 3ml OK 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 _

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 = 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 EndothermicExothermic Requires EnergyReleases Energy

Temperature How much thermal energy something has. K = C C = (F -32) 1.8 0C = Freezing Water 100C = boiling water 32F = freezing water 212F= boiling water 96F body temp 0K 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 = T final - T initial 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  T If q is positive it means the temperature goes up If 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