Welcome to the World of Chemistry : Welcome to the World of Chemistry Yale University Chemistry 113 Fall 2006: Prof. Victor S. Batista Spring 2007: Prof. Gary W. Brudvig
What does Chemistry concern with ? : What does Chemistry concern with ? WHAT MATTER IS ?
HOW CAN MATTER BE MADE ?
HOW DOES MATTER BEHAVE ?
Chemistry is the foundation of all molecular sciences
Chemistry provides understanding, prediction and control of the nature and behavior of matter
Chemistry is practical and profoundly philosophical
Chemistry & Matter : Chemistry & Matter We can explore the MACROSCOPIC world — what we can see —
to understand the PARTICULATE worlds we cannot see.
We perform EXPERIMENTS to explore these worlds.
(students are strongly encourage to take the lab 116L)
A Chemist’s View: Exp. I : A Chemist’s View: Exp. I 2 H2(g) + O2 (g)
--> 2 H2O(g)
Chemical Properties and Chemical Change : Chemical Properties and Chemical Change Chemical change or chemical reaction — transformation of one or more atoms or molecules into one or more different molecules. Burning hydrogen (H2) in oxygen (O2) gives H2O.
A Chemist’s View: Exp. II : A Chemist’s View: Exp. II Zn(s) + S (s) --> ZnS(s)
Scientific Method : Scientific Method (1) Question about some aspect of the world.
(2) Postulate a tentative explanation (hypothesis) and make predictions.
(3) Test those predictions against observations of reproducible events.
(4) Repeat steps 2 and 3 until there are no more discrepancies between predictions and observations.
When consistency is obtained hypotheses become a coherent set of propositions (a theory) that explain a class of phenomena.
Types of Observations and Measurements : Types of Observations and Measurements We make QUALITATIVE observations of reactions — changes in color and physical state.
We also make QUANTITATIVE MEASUREMENTS, which involve numbers.
Use SI units — based on the metric system
UNITS OF MEASUREMENT : UNITS OF MEASUREMENT Use SI units — based on the metric system
Length
Mass
Time
Temperature Meter, m Kilogram, kg Seconds, s Celsius degrees, ˚C
kelvins, K
Units of Length : Units of Length 1 kilometer (km) = ? meters (m)
1 meter (m) = ? centimeters (cm)
1 centimeter (cm) = ? millimeter (mm)
1 nanometer (nm) = 1.0 x 10-9 meter
1 angstrom (A) = 1.0 x 10-10 meter o o
Temperature Scales : Temperature Scales Fahrenheit
Celsius
Kelvin
Temperature Scales : Temperature Scales Notice that 1 K degree = 1 degree Celsius Boiling point of water Freezing point of water Celsius Kelvin Fahrenheit
Temperature Scales : Temperature Scales 100 oF = 38 oC = 311 K oF oC K 38 oC = (100 oF – 32 oF) * 100 oC / 180 oF
311 K = 273 K + 38 oC * 100 K / 100 oC Conversion Factor:
100 oC degrees per 180 oF degrees 32 oF = 0 oC = 273 K
Calculations Using Temperature : Calculations Using Temperature Generally require temp’s in kelvins
T (K) = t (˚C) + 273.15
Body temp = 37 ˚C + 273 = 310 K
Liquid nitrogen = -196 ˚C + 273 = 77 K
Physical Properties : Physical Properties What are some physical properties?
color
melting and boiling point
odor
Physical properties characterize the identity of pure substances salt sodium
Physical Changes : Physical Changes Some physical changes would be
boiling of a liquid
melting of a solid
dissolving a solid in a liquid to give a homogeneous mixture — a SOLUTION. Physical changes do not change the identity of Pure Substances
DENSITY - an important and useful physical property : DENSITY - an important and useful physical property 13.6 g/cm3 21.5 g/cm3 2.7 g/cm3 Physical properties, cont’d
Slide18 : Problem A piece of copper has a mass of 57.54 g. It is 9.36 cm long, 7.23 cm wide, and 0.95 mm thick. Calculate density (g/cm3). Density = mass ( g ) volume ( cm 3 )
Slide19 : Strategy
1. Get dimensions in common units.
2. Calculate volume in cubic centimeters.
3. Calculate the density.
Slide20 : SOLUTION
1. Get dimensions in common units.
2. Calculate volume in cubic centimeters.
3. Calculate the density.
(9.36 cm)(7.23 cm)(0.095 cm) = 6.4 cm3 Note only 2 significant figures in the answer! Conversion factor
Significant Figures : Significant Figures 57.54 g 4 significant figures
7.23 cm 3 significant figures
0.95 mm 2 significant figures
0.095 cm 2 significant figures
(zeros to the left of 9 simply
locate the decimal point)
600. g 3 significant figure
8000 kg 1 significant figure
100 cm/m infinte number of significant figures
(defined quantity)
DENSITY : DENSITY Density is an INTENSIVE property of matter.
does NOT depend on quantity of matter.
temperature
Contrast with EXTENSIVE
depends on quantity of matter.
mass and volume. Styrofoam Brick
PROBLEM: Mercury (Hg) has a density of 13.6 g/cm3. What is the mass of 95 mL of Hg? : 1. Convert volume to mass
PROBLEM: Mercury (Hg) has a density of 13.6 g/cm3. What is the mass of 95 mL of Hg? 2. Convert mass (g) to mass (lb) Inverse Problems
PROBLEM: Mercury (Hg) has a density of 13.6 g/cm3. What is the mass of 95 mL of Hg in grams? In pounds? : PROBLEM: Mercury (Hg) has a density of 13.6 g/cm3. What is the mass of 95 mL of Hg in grams? In pounds? Solve the problem using DIMENSIONAL
ANALYSIS.
PROBLEM: Mercury (Hg) has a density of 13.6 g/cm3. What is the mass of 95 mL of Hg? : Strategy
1. Use density to calc. mass (g) from volume.
2. Convert mass (g) to mass (lb)
Need to know conversion factor
= 454 g / 1 lb
PROBLEM: Mercury (Hg) has a density of 13.6 g/cm3. What is the mass of 95 mL of Hg? First, note that 1 cm3 = 1 mL