CMH 121 Luca Preziati Chapter 1: Matter, Energy, and Measurement Chemistry = The science that seeks to understand what matter does by studying what atoms and molecules do. DEF

CMH 121 Luca Preziati Chapter 1: Matter, Energy, and Measurement Observation = A way of acquiring information about nature. DEF Simple descriptions (qualitative observation) Number (quantitative observation) Hypothesis = A tentative explanation of your observations DEF Falsifiable: a test may invalidate your hypothesis Experiments = Tests of hypotheses, laws or theories DEF Results either Validate (confirm) or Invalidate (deny) your ideas Law = A statement that combines all past observations DEF Predict future observations You cannot choose to violate a scientific law Theory = An explanation that extends beyond individual observations to an understanding of the underlying causes for the way nature is or behaves DEF Models of nature

CMH 121 Luca Preziati Chapter 1: Matter, Energy, and Measurement Observations Hypothesis Law Theory Experiments

CMH 121 Luca Preziati Chapter 1: Matter, Energy, and Measurement Scientific Notation is a way of writing large and small numbers The sun’s diameter is 1,392,000,000 m An atom’s average diameter is m Large Number = Positive Exponent x 10 9 m Large Number = Positive Exponent x 10 9 m Small Number = Negative Exponent 3 x m Small Number = Negative Exponent 3 x m The sun’s diameter is x 10 9 m An atom’s average diameter is 3 x m

CMH 121 Luca Preziati Chapter 1: Matter, Energy, and Measurement Measurement = Quantitative observation DEF Comparison to an agreed upon standard Every measurement has a number and a unit Scientists have measured the average global temperature rise over the past century to be 0.6 °C The number tells you 1.what multiple of the standard the object measures 2.the uncertainty in the measurement The number tells you 1.what multiple of the standard the object measures 2.the uncertainty in the measurement The unit tells you what standard you are comparing your object to The unit tells you what standard you are comparing your object to

CMH 121 Luca Preziati Chapter 1: Matter, Energy, and Measurement Writing a number in scientific notation 1,392,000,000 m 1.Locate the decimal point 2.Move the decimal point until a number between 1 and 10 is obtained 3.Multiply the new number by 10 n 4.n is the number of places you moved the decimal point 5.Large number? n is positive Small number? n is negative 1,392,000,000. m 1.392,000,000. m x 10 ? 9 m x 10 9 m

CMH 121 Luca Preziati Chapter 1: Matter, Energy, and Measurement Significant Figures Writing Numbers to Reflect Precision Exact Values Can be obtained by counting or by definition Exact values have “unlimited significant figures” Measurements Are obtained from instruments The number of significant figures reflects the instrument precision. All the digits written are known with certainty except the last one, which is an estimate 1.2 grams Certain Estimated

CMH 121 Luca Preziati Chapter 1: Matter, Energy, and Measurement Counting Significant Figures 1.Write the number in scientific notation 2.Count the number of figures m 3.5 x m 2 Significant figures Note: Zeros at the end of a number without a written decimal point are ambiguous and should be avoided by using scientific notation. if 150 has 2 sig. figs. then 1.5 x 10 2 but if 150 has 3 sig. figs. then 1.50 x 10 2

CMH 121 Luca Preziati Chapter 1: Matter, Energy, and Measurement 1: Non zero digits are always significant. Thus 6.23 km has three significant figures. 2: Zeros in the middle of a figure are always significant. Thus g has 6 significant figures. 3: Zeros at the beginning of a number are only decimal place holders; they are not significant. Thus cm has three significant figures. 4: Zeros at the end of a number but after the decimal point are significant. Thus mL has four significant figures. 5: Zeros at the end of a number but before the decimal point are ambiguous. Thus 21,000 kg has 2 significant figures, but 21,000.0 has 6 significant figures (rule 4). Counting Significant Figures

CMH 121 Luca Preziati Chapter 1: Matter, Energy, and Measurement How many significant figures are in each of the following numbers? × dozen = Counting Significant Figures. Examples.

CMH 121 Luca Preziati Chapter 1: Matter, Energy, and Measurement Multiplication and Division with Significant Figures When multiplying or dividing measurements with significant figures, the result has the same number of significant figures as the measurement with the fewest number of significant figures 5.02 × 89,665 × 0.10= = 45 3 sig. figs. 5 sig. figs. 2 sig. figs. 2 sig. figs ÷6.10= = sig. figs. 3 sig. figs. 3 sig. figs.

CMH 121 Luca Preziati Chapter 1: Matter, Energy, and Measurement Addition and Subtraction with Significant Figures When adding or subtracting measurements with significant figures, the result has the same number of decimal places as the measurement with the fewest number of decimal places = = dec. pl. 3 dec. pl. 3 dec. pl. 2 dec. pl = = dec. pl 3 dec. pl. 1 dec. pl.

CMH 121 Luca Preziati Chapter 1: Matter, Energy, and Measurement The Standard Units Scientists have agreed on a set of international standard units for comparing all our measurements called the SI units Système International = International System QuantityUnitSymbol lengthmeterm masskilogramkg timeseconds temperaturekelvinK

CMH 121 Luca Preziati Chapter 1: Matter, Energy, and Measurement Common Prefixes in the SI System PrefixSymbol Decimal Equivalent Power of 10 mega-M1,000,000Base x 10 6 kilo-k 1,000Base x 10 3 deci-d 0.1Base x centi-c 0.01Base x milli-m 0.001Base x micro-µ or mc Base x nano-n Base x 10 -9

CMH 121 Luca Preziati Chapter 1: Matter, Energy, and Measurement 1 mile = km1 km = miles 1 foot = cm1 m = inches 1 inch = 2.54 cm1 cm = inches 1 mm = inches Length = Measure of the two-dimensional distance an object covers SI unit = meter About 3½ inches longer than a yard 1 meter = one ten-millionth the distance from the North Pole to the Equator = distance between marks on standard metal rod in a Paris vault = distance covered by a certain number of wavelengths of a special color of light Commonly use centimeters (cm) DEF

CMH 121 Luca Preziati Chapter 1: Matter, Energy, and Measurement Volume = Measure of the amount of three-dimensional space occupied SI unit = cubic meter (m 3 ) a Derived Unit Commonly measure solid volume in cubic centimeters (cm 3 ) 1 m 3 = 10 6 cm 3 1 cm 3 = m 3 = m 3 Commonly measure liquid or gas volume in milliliters (mL) DEF 1 gallon = L1 Liter = gallon 1 quart = L1 liter = quarts 1 cup = L1 liter = fl oz 1 fl oz = mL1 liter = 61 cu. inches

CMH 121 Luca Preziati Chapter 1: Matter, Energy, and Measurement Mass = Measure of the amount of matter present in an object SI unit = kilogram (kg) about 2 lbs. 3 oz. Commonly measure mass in grams (g) or milligrams (mg) DEF 1 pound = g1 kg = lbs 1 oz = g1 g = oz. 1 grain = g1 g = grains

CMH 121 Luca Preziati Chapter 1: Matter, Energy, and Measurement Time SI unit = second (s) 60 s in 1 minute 60 minutes in hour A second is defined as the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom at zero Kelvin. This is the basis for the so-called atomic clocks.

CMH 121 Luca Preziati Chapter 1: Matter, Energy, and Measurement Temperature = measure of the average kinetic energy of the molecules in a sample SI unit = Celsius (°C) DEF WaterFahrenheitCelsiusKelvin Freezing point Boiling Point

CMH 121 Luca Preziati Chapter 1: Matter, Energy, and Measurement Density Ratio of mass:volume Solids = g/cm 3 1 cm 3 = 1 mL Liquids = g/mL Gases = g/L Volume of a solid can be determined by water displacement – Archimedes Principle Density : solids > liquids >>> gases except ice; it is less dense than liquid water! DEF

CMH 121 Luca Preziati Chapter 1: Matter, Energy, and Measurement Arrange conversion factors so starting unit cancels Arrange conversion factor so starting unit is on the bottom of the conversion factor May string conversion factors So we do not need to know every relationship, as long as we can find something else the beginning and ending units are related to unit 1 unit 2 unit 1 unit 2x= Problem Solving and Dimensional Analysis unit 1 = unit 2

CMH 121 Luca Preziati Chapter 1: Matter, Energy, and Measurement Dimensional Analysis Exercise 1: Convert 7.8 km to miles 1.Write down the Given quantity and its unit Given:7.8 km 2.Write down the quantity you want to Find and unit Find:? miles 3.Write down the appropriate Conversion Factors Conversion Factors: 1 km = mi 4.Write a Solution MapSolution Map: 5.Follow the Solution Map to Solve the problem Solution: 6.Sig. Figs. and RoundRound: mi = 4.8 mi 7.CheckCheck:Units & Magnitude are correct kmmi

CMH 121 Luca Preziati Chapter 1: Matter, Energy, and Measurement Precision (reproducibility) refers to how close measurements in a series are to each other. Accuracy refers to how close a measurement is to the actual value. Systematic error produces values that are consistently higher or lower than the actual value. Systematic error can be reduced or eliminated by calibration or comparison with a known standard. Random error produces errors that are higher and lower than the actual value with no recognizable pattern. Precision and Accuracy

CMH 121 Luca Preziati Chapter 1: Matter, Energy, and Measurement Precision and Accuracy

CMH 121 Luca Preziati Chapter 1: Matter, Energy, and Measurement Measurements Are obtained from instruments The number of significant figures reflects the instrument precision. All the digits written are known with certainty except the last one, which is an estimate 1.2 grams Certain Estimated

CMH 121 Luca Preziati Chapter 1: Matter, Energy, and Measurement DEF Matter = anything that occupies space and has mass Matter

CMH 121 Luca Preziati Chapter 1: Matter, Energy, and Measurement Energy DEF Energy = anything that has the capacity to do work Law of Conservation of Energy: “Energy can neither be created nor destroyed” Kinetic Energy is energy of motion, or energy that is being transferred from one object to another Potential Energy is energy that is stored We cannot get a 100% efficient energy transformation process

CMH 121 Luca Preziati Chapter 1: Matter, Energy, and Measurement Heat (q) Heat = exchange of thermal energy between samples of matter heat flows from the matter that has high temperature to matter that has low temperature until they reach the same temperature heat is exchanged through molecular collisions between two samples OR through radiation DEF

CMH 121 Luca Preziati Chapter 1: Matter, Energy, and Measurement Specific Heat Capacity Specific Heat is the amount of energy required to raise the temperature of one gram of a substance by one Celsius degree the larger a material’s specific heat is, the more energy it takes to raise its temperature a given amount like density, specific heat is a property of the type of matter it doesn’t matter how much material you have it can be used to identify the type of matter water’s high specific heat is the reason it is such a good cooling agent it absorbs a lot of heat for a relatively small mass Amount of Heat = Mass x Heat Capacity x Temperature Change q = m x C x  T