1. Chapter 2
Matter and Energy

2. 1) What is the relationship between matter and energy?
Unit essential questions:
1) What is the relationship between matter and energy?
2) How is matter studied and what is necessary to perform these studies?

3. What is energy and what forms does it take?
Lesson Essential Question:
What is energy and what forms does it take?

4. Section 1: Energy Energy: the capacity to do work.
Whenever matter changes, energy is involved!
Can be endothermic or exothermic.
Endothermic – energy is absorbed
Exothermic – energy is released
Work means something different here than how we usually use the word. Work, in chem and physics, is the ability to bring about some sort of change. Could be sharpening your pencil- changing location of your hand, changing shape of pencil. Could be baking a cake- combining ingredients, mixing, oven provides heat. From Chapter 1, you should already understand physical vs chemical changes. Endothermic (think “IN”) and exothermic (think “OUT”). Exoskeleton- outside skeleton. Exo = out; endo = in.

5. Law of Conservation of Mass(Matter)/Energy
Energy (E) cannot be created or destroyed, only transferred. (The same is true for matter!)
*This is what happens in a chemical or
physical change.
System – all components being studied
Surroundings – everything outside the system
Energy is transferred between system and surroundings
E can be changed into other forms of E.
Ex: Light, heat, chemical, mechanical, electrical, sound
This law is also thought of as ‘Law of conservation of mass’. Remember that this applies to physical or chemical changes, not nuclear reactions (many think of a nuclear bomb, etc.). The idea of energy being transferred is important as is the forms that energy can be.

6. Energy as Heat
Heat – energy transferred between two objects at different temperatures
Always transferred from high E (hotter object) to low E (cooler object)
Kinetic energy – energy of motion
Temperature – measure of average kinetic energy of particles in the object
Kelvin scale – SI unit
Absolute zero = no kinetic energy
K = oC
Many people confuse temperature and heat. Heat is a transfer between TWO objects, while temperature is the measure of kinetic energy of ONE object. We will measure temperature in Celsius, but we will usually convert it to Kelvin for most calculations.

7. Heat vs. Temperature
Addition of heat does not always change temperature
Example: boiling water
Adding more heat at the boiling point does not cause it to change temperature
So what is happening to the energy being transferred to the water at the boiling point?
Think about what happens to water molecules at the boiling point.
Phase change!
As heat is added to water, this causes the temperature of the water to increase. This also causes the motion of water molecules to increase (higher temperature = faster motion of molecules). But, at the boiling point, the heat energy is used to convert water from liquid to gas, rather than as motion with respect to the molecules. Recall how we discussed the interaction of molecules in each phase- solid had the most and gas the least (little to none). We will talk about this more- intermolecular forces of attraction- later, but the energy at melting and boiling points breaks apart these intermolecular forces, which allows for phase changes to occur.

8. Heating/Cooling Curve
No temperature change = state change
Temperature change = change in molecular motion (kinetic energy)
Notice on the graph – the areas where the lines are horizontal are the places where changes of state occur. Energy is being added as heat, but the temperature does not change. The energy is going into the matter to break apart molecules or atoms instead of as kinetic energy (temperature). Once the change of state has occurred, the temperature will begin to rise.

9. Specific Heat
Quantity of heat required to raise one gram of a material 1 K (or 1 oC)
SI unit for energy = Joule (J)
Units for specific heat = J/(g∙oC) or J/(g∙K)
Metals = low specific heats- they heat up/cool down easily!
Aluminum: 0.897J/g∙K
Copper: 0.385J/g∙K
Gold: 0.129J/g∙K
Water = high specific heat- does not heat up/cool down as easily: 4.18J/g∙K
Specific heat is basically how much energy it takes to change the temperature of an object. Some types of matter heat up/cool down quickly (like metals) while others heat up and cool down slowly (like water). This can be used for advantages like cooking materials.

10. Calculating Specific Heat
What do we need to know to calculate specific heat?
Formula: Cp = q / (m x T)
Note: T = Tf – Ti (change in anything is always final minus initial)
E added as heat, mass, & T
We will learn to solve for Cp or for q depending on the problem. We can even solve for m or T. We will do a lab experiment using water and aluminum.

11. How are ideas and questions approached in science?
Lesson Essential Question:
How are ideas and questions approached in science?

12. Scientific Method Form Hypothesis Test Hypothesis Analyze Results
Draw Conclusions
Publish Results
Construct a Theory
Revise hypothesis
Ask Questions
Make Observations
Notice how some of the boxes have multiple arrows. At almost any step, you can start the process over by revising the hypothesis.

13. Experiments
Hypothesis – a prediction or educated guess as to what will happen.
Represents cause and effect- ‘if, then’ statement
Testing
Variable – factor that could effect results
Change only 1 at a time
Control – variable that is kept constant
Many of these in experiment.
Theory – explains why things happen.
Repeated testing needed
Based on lots of data and observations
A hypothesis is not a question, but a statement that predicts what you think will happen based on observations so far. When testing, you can have more that one variable, but you need to change 1 at a time so that you can determine what is causing the results. When a variable is not changed, this is called the control. A theory tells why the results happened.

14. Laws Law – a summary or description of events
Tells how things work, not why
Helps predict events/behavior (because they follow a pattern according to the law)
Law of conservation of mass – mass cannot be created or destroyed in ordinary physical or chemical changes
Same as law of conservation of energy
Model – represents an object, a system, a process, or an idea.
Computer generated, 3D, drawing, etc.
A law describes the event; it can be a mathematical formula or a statement. It does not explain WHY it happens (like a theory does). We will do an experiment to test the Law of conservation of mass. Models can be very useful for chemistry since we cannot see atoms, etc. The models gives us a picture so we can see what is happening.

15. Theories vs. Laws Planets move in an ellipse with a star at a focus.
The amount of disorder in an isolated system never decreases.
The universe was created when a massive explosion occurred.
As the pressure of a gas increases, the volume of the gas decreases.
Continents developed from one massive continent (Pangaea) where they broke apart and moved due to tectonic plates in the Earth’s lithosphere.
Kepler’s 1st Law- describes motion of planets.
2nd Law of Thermodynamics- describes chaos.
Big Bang Theory- explains where
universe & planets came from.
Boyle’s Law- describes P & V effect on gases.
Plate Tectonics Theory – explains where continents came from.

16. How do we obtain the correct number of digits in calculations?
Lesson Essential Questions:
How do we obtain the correct number of digits in calculations?
How are very small or large numbers represented?

17. Section 3: Measurements & Calculations in Chemistry
Accuracy vs. Precision
Accuracy – how close a measurement is to the true/correct value
Precision – how close several measurements are to each other
Notice the diagram for examples. The first is accurate because the average of the locations of the darts is in the bulls-eye (but each dart is not accurate). You can also have poor accuracy and poor precision if you do not hit the bulls-eye and have a wide range of hits on the target. Ask a student to come up to the board and draw an example of what poor accuracy and poor precision would look like.

18. Introduction to Sig Figs
Use the ‘ruler’ to measure the width of your table. Use each ‘side’ of the ruler to make the measurements. You should have a total of four measurements.
Record these on a piece of paper. Include units!
Each side should have the following number of decimal places:
#1: 1 #2: #3: 1 #4: 2
Helps students to compare accuracies of numbers that are similar, and to see the importance of accuracy in terms of sig figs.

19. Significant Figures (significant digits)
D = 3.421g/5.957mL = …g/mL
How do we know where to round?
Significant Figures are all digits known with certainty plus one more uncertain/estimated digit.
Rules that govern how you determine where to “cut off” a number
Calculators do not “know” these rules, so it’s up to YOU to know where to round!
Also helps to show degrees of accuracy and precision- more sig figs = better accuracy and also helps multiple measurements be precise!
Significant really means measured. If we are able to get the number from a measuring device than the number is significant – it matters to us. We do not count numbers that we cannot tell if they were measured or estimated. This is an extremely important concept – you will lose a great number of points over the course of the year if you do not grasp this concept. Take the time to study the rules and learn them now. It will greatly help you!!

20. Rules for determining significant digits
Rule #1: Nonzero digits are always significant.
46.3 m sig figs
6.295 g
Rule #2: Zeros between significant digits (typically nonzero digits) are significant.
40.7 L sig figs
87,009 km
Rule #3: Zeros in front of nonzero digits are not significant.
m sig figs kg
4 sig figs
5 sig figs
We will practice this with homework. Notice the units on each of the numbers – this can also tell us if the number was measure or simply counted. Numbers that are counted are said to infinite sig figs since they are exact.
1 sig fig

21. Rules for sig figs continued…
Rule #4: Zeros both at the end of a number AND to the right of the decimal are significant.
85.00 g sig figs cm
Rule #5: Zeros at the end of a number but to the left of a decimal point may or may not be significant.
*If a zero has not been measured or estimated, it is not significant.
*A decimal point placed after zeros indicates that the zeros are significant.
2000 m sig fig
2000. m
10 sig figs
We will discuss scientific notation at the end of this section. It is actually easier to use for sf since whatever is in front of the “x” is significant (regardless of the rules!).
4 sig figs

22. Rules for sig figs continued…
Sig figs & scientific notation
If a number is written in scientific notation, only look at the first number for sig figs!
The x10Y does not impact sig figs- it only changes size!
2.0 x 103m
3.041 x 10-2g
2 sig figs
We will discuss scientific notation at the end of this section. It is actually easier to use for sf since whatever is in front of the “x” is significant (regardless of the rules!).
4 sig figs

23. Rules for Using Significant Figures in Calculations
1) In multiplication and division problems, the answer cannot have more sig figs than there are in the measurement with the least sig figs.
*Look for the # with the least sig figs!
Ex: m
x m
m round off to 4 sig figs
= m2
6 sig figs
If you followed how to multiply numbers, you would see that the last digit in each measurement would cause ‘error’ up to the 4 sf. This is why the rule is to use the least significant figures.
4 sig figs

24. Rules for Calculating continued…
2) In addition and subtraction, the result can be no more certain than the least certain number in the calculation.
* Look for the # with the least decimal places!
Ex: g
2.879 g g
g round to 1 decimal place
= g
2 decimal places
3 decimal places
For addition, it’s a little easier to see how sf works – you can draw a line from the least decimal place to see where to cut it off.
1 decimal place

25. Finally… Ex: 7.92g – 8.5g2 = 7.92g – 3.5g = 4.4g 2.46g
3) If a calculation has addition/subtraction and multiplication/division, round after each operation. 4) In chemistry you will follow sig fig rules to know where to round off all of your calculations.
Ex: 7.92g – 8.5g2
= g – 3.5g
= 4.4g
2.46g
This can be difficult to remember to do and makes things complicated, luckily we do not have many problems where we have both types of calcualtions!! 

26. Unlimited Significant Figures
Numbers that are exact or counted have infinite sig figs.
Have no impact in determining sig figs in an answer from a calculation.
Examples:
35 cars = infinite sf counted!
1 m = 1000 mm exact!
Conversion factors often have infinite sig figs!
Any number usually given in a problem has sf – this helps to narrow down the numbers you should analyze for sf. Any number that is used to convert (conversion factor) will not be part of the sf determination.

27. Average distance between sun and earth: 93,000,000 miles
Warm-Up!
Is there an easier way to write such large and small numbers ??
YES!
Average distance between sun and earth: 93,000,000 miles
Diameter of an atom: m
Imagine you wanted to measure the distance in between planets of our solar system and the diameter of an atom. What would the size of your measurements look like?

28. Scientific Notation
Very large or very small numbers are easier to write using scientific notation.
Form = M x 10y
M = number between 1 and 10 (not including 10!)
y = integer (can be positive or negative)
Examples:
m/s =
cm3 =
4500. g =
6.79 x 10-7m =
5.307 x 105L =
Follow sig figs when calculating!
2.998 x 108 m/s
1.23 x 10-6 cm3
Look on your calculator for EE or EXP button to put a number in scientific notation. You may need to use your 2nd function key if it is written above another key. Put your number first, then hit the EE button, followed by the power of ten. Hit enter, and you’ll get the number written out. To change between scientific notation and “normal” – look for a SCI or MODE button (TI 83 Plus: mode, move curser one to the right onto ‘Sci’, and hit enter. Any numbers entered in will be in scientific notation. To get back to normal, do the same but choose ‘Normal’.). We will go over this in class, be sure to bring YOUR calculator so we can do it together!
4.500 x 103 g m
530,700L