Chemistry SM-1131 Week 3 Lesson 2

1. Chemistry SM-1131Week 3 Lesson 2 Dr. Jesse Reich Assistant Professor of Chemistry Massachusetts Maritime Academy Fall 2008

2. Class Today • Friday • Wiki • Matter- physical v. chemical, physical changes v. chemical changes • Separating Matter • Wednesday = Energy and Temperature, maybe some problems

3. 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!

4. Density • Density = Mass volume d = m v

5. 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!

6. 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.

7. Solid, Liquid, Gas _

8. 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.

9. 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.

10. Homogeneous Mixture

11. Heterogeneous Mixture

12. New Material • Chemical v Physical • Energy

13. Properties • Properties: The characteristics we use to distinguish one substance from another. • Chemical vs. Physical properties

14. 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.

15. 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!

16. 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.

17. Evidence of Chemical RXNs • Odor • Color Changes • Heat and Light • Sound • Bubbling • Explosions

18. 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.

19. Conservation of Mass • There is a chemical law: Mass is neither created nor destroyed in a chemical reaction.

20. Energy • “The capacity to do work” • Energy is conserved: ie it is neither created nor destoryed

21. Kinetic Energy • Energy in motion

22. Potential Energy • Stored energy that could “potentially” be released

23. Electrical Energy • Energy associated with the flow of electrons.

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

25. 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

26. You should practice converting units • 23 Cal into cal • 45 joules into Cal • 3 kWh to cal

27. 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.

28. Endothermic and Exothermic Requires Energy Releases Energy Endothermic Exothermic

29. Temperature • How much thermal energy something has. • K = C + 273 • 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.

30. 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.

31. Calculating Heat Capacity • Heat = Mass x Specific Heat Capacity x Temp Change q = m x C x DT DT = 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 DT If q is positive it means the temperature goes up If q is negative it means the Temp went down.

32. 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.

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

34. Extra Time • Heat = Mass x Specific Heat Capacity x Temp Change q = m x C x DT • 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