Ma)er, Energy, And Measurement. What is Chemistry? The Study of Chemistry 8/18/09. Chapter 1

Transcription

1 Ma)er, Energy, And Measurement Chapter 1 What is Chemistry? Chemistry is the study of the structure and proper@es of ma)er and the transforma@ons from one form of ma)er to another Ma)er is defined as anything that has mass and take up space The Study of Chemistry Proper@es of Ma)er Physical Proper@es (color, density, boiling point) Chemical Proper@es (flammable, water reac@ve) Changes of Ma)er Physical Changes (boiling, mel@ng, dissolving) Chemical Changes (burning, corroding) 1

2 The Method About 1600 the method came into use Hypothesis, Test by Revise, Retest Terms associated with the method Fact: Law: Hypothesis: Theory: and Numbers Number are found in science due to measurements Big and small numbers are wri)en in or 12,400,000 m would be wri)en as 1.24 x 10 7 m g would be wri)en as 3.44 x 10 6 g Scien@sts and Numbers Measurements involve instruments Instruments have precision In order to show the precision: A numeric measurement is always read to one digit beyond the last certain digit = digit of uncertainty The last digit in any measurement you see is always the digit of uncertainty All certain digit and the digit of uncertainty are called significant figures 2

3 When measuring anything on a digit instrument record all digit on the display the last one is the digit of uncertainty When measuring with a ruler, graduated cylinder, etc. Read on digit beyond the last mark Significant Figures Significant Figures When you are determining the significant figure in a measurement keep in mind the following: Nonzero digits are always significant Zeros at the beginning of a number are never significant Zero between nonzero digits are always significant Zero at the end of a number that contains a decimal are significant Zero at the end of a number that does not contain a decimal may or may not be significant Significant Figures: Examples 3

4 Units of Measurement Units ID what a number means Chemistry using the SI system The SI system using the metric concept of a prefix plus a base unit (prefix: page 9) Units of Measurement More on Temperature 4

5 More on Temperature Temperature Units: o F is common o C is based on 0 o C being the freezing point of water and 100 o C being the boiling point of water Conversion to o C is done by o C = 5/9( o F 32) K is based on the concept of absolute zero Absolute zero is 0K which equal o C Conversion to Kelvin is done by o C =K Measurement Conversions The handy way to convert on unit to another is called: dimensional analysis factor label method The system is based on the idea that: Using Conversion Factors 2.54cm = 1inch 4qt = 3.785L Note: Unit conversion factors carry sig figs but they are equal to the part of the conversion with the greater number of digits (some factors are exact) 5

6 Common Conversion Factors Example Show the conversion of each of the following: Example Show the conversion of each of following double units: 6

7 Solid Liquid Gas State of Ma)er Defined as: Mass per unit volume Units: Solid: Liquid: Gases: Density Density Uses of density: To ID substance To determine a mass given a volume To determine volume given mass Calcula@ons: Equa@on: d =m/v Mass / volume = density Volume x density = mass Mass / density = volume 7

8 Examples Examples Examples 8

9 Specific Gravity Specific gravity is the same as density but has no units The reason for specific gravity is defined as a comparison to the density of water, which is considered the standard The density of lead is 7.86g/mL and the density of water is 1.00g/mL therefore the specific gravity of lead is 7.86 Specific gravity is oken measured with a hydrometer. A hydrometer is a weighted glass bulb with stem that is marked with a line of 1 in pure water. Specific Gravity Energy Energy is the capacity to do work Poten@al energy: stored energy Examples: chemical, nuclear, posi@onal Kine@c energy: the energy of mo@on Examples: heat, light, electricity Law of Conserva@on of Energy: Energy can either be created nor destroyed 9

10 Heat Heat is the most common energy associated with chemistry Temperature is Specific Heat Specific Heat: is the amount of energy needed to raise the temperature of 1 gram of a specific substance 1 o C Substances that get hot fast usually have a low specific heat Some common specific heat values are found on page 22 Specific Heat Calcula@ons: Amount of heat = SH x m x ΔT Example: 10

11 Body Temperature: 37 o C or 98.6 o F If the outside temperature is colder than body temperature the body loses heat Extreme lose of heat: hypothermia If the outside temperature is too high the body sweats to cool itself Extreme high temperature or fever: hyperthermia 11