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Chapter 2Matter and Energy
1) WHAT IS THE RELATIONSHIP BETWEEN MATTER AND ENERGY?
UNIT ESSENTIAL QUESTIONS:
2) HOW IS MATTER STUDIED AND WHAT IS NECESSARY TO PERFORM THESE STUDIES?
WHAT IS ENERGY AND WHAT FORMS DOES IT TAKE?
Lesson Essential Question:
Section 1: EnergyEnergy: the capacity to do work.
◦Whenever matter changes, energy is involved! Can be endothermic or exothermic.
Endothermic – energy is absorbed Exothermic – energy is released
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
Energy as HeatHeat – energy transferred between
two objects at different temperatures◦Always transferred from high E (hotter
object) to low E (cooler object)Kinetic energy – energy of motionTemperature – measure of average
kinetic energy of particles in the object◦Kelvin scale – SI unit◦Absolute zero = no kinetic energy◦K = oC + 273.15
Heat vs. TemperatureAddition 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!
Heating/Cooling Curve
Temperature change = change in molecular motion (kinetic energy)
No temperature change = state change
Specific HeatQuantity 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
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
HOW ARE IDEAS AND QUESTIONS APPROACHED IN SCIENCE?
Lesson Essential Question:
Scientific MethodForm
Hypothesis
Test Hypothesi
s
Analyze Results
Draw Conclusio
ns
Publish Results
Construct a Theory
Ask Question
s
Make Observati
ons
Revise hypothes
is
ExperimentsHypothesis – a prediction or educated
guess as to what will happen.◦Represents cause and effect- ‘if, then’
statementTesting
◦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
LawsLaw – 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.
Theories vs. LawsPlanets 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.
HOW DO WE OBTAIN THE CORRECT NUMBER OF DIGITS IN CALCULATIONS?
Lesson Essential Questions:
HOW ARE VERY SMALL OR LARGE NUMBERS REPRESENTED?
Section 3: Measurements & Calculations in ChemistryAccuracy vs. Precision
◦Accuracy – how close a measurement is to the true/correct value
◦Precision – how close several measurements are to each other
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: 1 #3: 1 #4: 2
Significant Figures (significant digits)D = 3.421g/5.957mL = 0.5742823568…
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!
Rules for determining significant digitsRule #1: Nonzero digits are always
significant.◦ 46.3 m 3 sig figs◦ 6.295 g
Rule #2: Zeros between significant digits (typically nonzero digits) are significant.
◦ 40.7 L 3 sig figs◦ 87,009 km
Rule #3: Zeros in front of nonzero digits are not significant.
◦ 0.009 587 m 4 sig figs◦ 0.000 09 kg
4 sig figs
5 sig figs
1 sig fig
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 4 sig figs◦ 9.070 000 000 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 1 sig fig 2000. m
10 sig figs
4 sig figs
Rules for sig figs continued…
Sig figs & scientific notationIf 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
4 sig figs
Rules for Using Significant Figures in Calculations1) 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: 12.2257 m x 1.162 m14.2062634 m2 round off to 4 sig figs
= 14.21 m2
6 sig figs4 sig figs
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: 3.95 g 2.879 g + 213.6 g 220.429 g round to 1 decimal place = 220.4 g
2 decimal places
3 decimal places
1 decimal place
Finally…
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 2.46g
= 7.92g – 3.5g
= 4.4g
Unlimited Significant FiguresNumbers 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!
Warm-Up!
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?
Average distance between sun and earth: 93,000,000 miles
Diameter of an atom: 0.000 000 000 062 m
Is there an easier way to write such large and small numbers ??YES
!
Scientific NotationVery 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:
◦ 299 800 000 m/s =◦ 0.000 001 23 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
4.500 x 103 g
0.000 000 679m
530,700L
