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Introduction to General Chemistry Part 2: Units Ch. 1 Qualitative and Quantitative Analysis • In chemistry, the scientific method is used to investigate scientific phenomena & acquire new knowledge • Empirical evidence is gathered which supports or refutes a hypothesis • Empirical evidence is either quantitative or qualitative – Quantitative data is numerical, and results can be measured – Qualitative data is NOT numerical, but consists of observations and descriptions Quantitative and Qualitative Analysis A+B Quantitative data • How much C is formed? • How efficient is the reaction? • What is the rate of the reaction? C Qualitative data • What color is it? • Is it solid, liquid, gas? • How does it smell? Units • Quantitative measurements are represented by a: NUMBER and a UNIT • A unit is a standard against which a physical quantity is compared physical quantity – Temperature is measured in Co, Ko,or Fo – Currency is measured in $USD – Distance is measured in meters, miles, ft, etc. – Time is reported in seconds, minutes, hr, etc. • Internationally accepted system of measurements is called the SI unit system SI Unit System: The Units of Physical Science Greek Prefixes • Prefixes indicate powers of 10 – ex. k= 103; 5 kg = 5 x (103)g A Review of Scientific Notation Scientific notation indicates a factor (F) multiplied by a power (n) of 10 F x 10n • Important: All integers end with a decimal point, even though it is not commonly written (1 1. ) • For all non integers, simply shift the decimal right n places 2.5 x 105 = 250000. 1.8773 x 108 = 187730000. • For negative exponents, shift the decimal left. All values less than 1 have negative exponents. 7.141 x 10-2 = .07141 3.867 x 10-7 = .0000003867 Convert to standard notation • 3.4912 x 104 • 8.971 x 10-3 • 6.50 x 100 Convert to scientific notation • 15 • 125.3 • 0.003003 Group Work Convert the following values to grams in both standard and scientific notation. – 421.4 kg – 1170.1 mg – 481 µg Why Are Units Important? Example #1 • In 1999, NASA lost the $125M Mars Orbiter System. • One group of engineers failed to communicate with another that their calculated values were in English units (feet, inches, pounds), and not SI units. • The satellite, which was intended to monitor weather patterns on Mars, descended too far into the atmosphere and melted. Why Are Units Important? Example #2 • In 1983, an Air Canada Plane ran out of fuel half way through its scheduled flight. Why? • Airline workers improperly converted between liters and gallons. • Luckily, no one died. Derived SI Units: VOLUME • Many measured properties have units that are combinations of the fundamental SI units • Volume: defines the quantity of space an object occupies; or the capacity of fluid a container can hold – expressed in units of (length)3 or Liters (L) – 1 L is equal to the volume of fluid that a cube which is 10 cm on each side can hold V = (10 cm)3 = 1000 cm3 1 L = 1000 cm3 10 cm 1000 mL = 1000 cm3 10 cm 10 cm mL = cm3 Derived SI Units: DENSITY • All matter has mass, and must therefore occupy space. Density correlates the mass of a substance to the volume of space it occupies. • Density = mass per unit volume (mass/volume). Different materials have different densities. Would a 20-gallon filled with bricks same mass as an volume of feathers? container have the equivalent NO! g feather 0.025 3 cm g brick 1.90 3 cm THE DENSITY OF WATER IS 𝟏 𝒈 𝒄𝒎𝟑 𝒐𝒓 𝟏 𝒈 𝒎𝑳 Group Work • A cubic container that is 25 cm on each side is filled with ethanol. The density of ethanol is 0.79 g/mL. – What is the volume of ethanol in the cube in mL? – What is the volume in L? – What is the mass of ethanol in kg? Give answers in scientific notation!! Derived SI Units: ENERGY • What is Energy? – Energy is defined as the capacity to perform “work” • How do we define work? • Work is defined as the action of applying a force acting over some distance. Work can not be done if no energy is available. • In SI units, we use the unit Joule (J) to represent energy. 𝑘𝑔 𝑚2 𝐽= 𝑠2 Conservation of Energy Energy is never created or destroyed, merely converted between forms and transferred from place to place. The total energy of the universe is finite. Forms of Energy • Energy comes in many forms and can be converted from one form to another. Some examples are given: • Chemical Energy – Energy stored in chemical bonds (e.g. gasoline, coal, etc.) that can be released by chemical reaction, typically combustion (fire) • Heat Energy (thermal energy) – Heat is defined as energy flow between bodies of matter resulting from collisions of molecules or random motions of electrons. Forms of Energy • Mass Energy – Energy and mass are interchangeable. During a fusion reaction (e.g. stars), mass is lost and energy is formed. This mass appears as energy according to the following: 𝐄 = ∆𝐦𝐜 𝟐 where m is the change in mass (in kg), c is the speed of light, and E is the energy released (J). This is the basis of nuclear power. • Kinetic Energy – Energy of motion (e.g. a moving car). An object with mass m, moving at a velocity V (meters/sec) has kinetic energy: 𝟏 𝐄𝐤 = 𝐦𝐕 𝟐 𝟐 Forms of Energy • Potential Energy – Potential energy corresponds to energy that is stored as a result of the position of mass in a field. • If a mass m is held at a height h (meters) above the ground, assuming a gravitational acceleration of 9.8 m/s2 (g), its potential energy is: 𝐄𝐏 = 𝐦𝐠𝐡 – If the object is dropped, it loses potential energy. However, it speeds up as it falls, so its kinetic energy increases equally (conversion). Forms of Energy • Electrical Energy – Energy resulting from electric current, the movement of electrons through a conductive circuit. Electrical energy is a type of potential energy. For a charge q (coulombs, C) moving across a voltage, V 𝐄𝐞𝐥𝐞𝐜 = 𝐪𝐕 • Light/Radiation – The energy of a wave of light is calculated as the product of Planck’s constant, h (J s), and the wave frequency, ν (1/s) 𝐄 = 𝐡𝐯 Power • It is often necessary to express the rate of energy usage. This is called power. 𝐞𝐧𝐞𝐫𝐠𝐲 𝐏𝐨𝐰𝐞𝐫 = 𝐭𝐢𝐦𝐞 • Typically, we speak in terms of energy per second. In SI units, a joule per second (J/s) is known as a watt (W). Temperature • Temperature: a measure of the tendency of a substance to lose or absorb heat. Temperature and heat are not the same. • Heat always flows from bodies of higher temperature to those of lower temperature – The stove top is ‘hot’ because the surface is at a much higher temperature than your hand, so heat flows rapidly from the stove to your hand – Ice feels ‘cold’ because it is at a lower temperature than your body, so heat flows from your body to the ice, causing it to melt Temperature • When performing calculations in chemistry, temperature must always be converted to Kelvin (oK) units (unless otherwise stated). • The lowest possible temperature that can ever be reached is 0oK, or absolute zero. At this temperature, all molecular motion stops. • To convert temperatures to the Kelvin scale: oK : oC + 273.15