The Meaning Of Chemistry

Transcription

1 The Meaning Of Chemistry Experiences and observations alone never lead to finalities. Theory, however, creates reliable roads over which we may pursue our journeys through the world of observation. Anton Reiser 1930

2 What is Science and What is Chemistry? Science is an organized and classified body of knowledge. Scientist systematically record information from observations, experiments, and discoveries to the physical world. Chemistry is a branch of science that studies the composition of substances and the changes that take place in their composition

3 Why is Chemistry Important? The world is a world of chemistry. Through chemistry we can understand and appreciate the changes that take place around us in the variety of natural and manmade substances. Knowledge of chemistry helps you to understand everyday phenomena such as burning wood and nuclear power.

4 What else? Through chemistry we can create totally new products such as orlon, nylon, and rayon fibers, develop useful substitutes for wood and ordinary metals with such materials as plastics and alloys, and improve a variety of familiar products such as fertilizers, paints, rubber, and insecticides.

5 Okay, what else? Chemistry enables us to solve many critical problems facing the world today such as Atomic waste disposal Reduction and elimination for air pollution Increasing pure water availability Cancer research and treatment New metals for rockets, missiles, and jet aircraft

6 What is the difference between Energy and Matter? Examine your books, clothing, money, and desks. What two characteristics do all of those items have in common? Occupy space Have weight

7 Clarify It! Inertia is the quality to keep an object moving in a fixed direction unless acted upon by an outside force such as friction Mass is the measure of inertia of a body. Matter is anything which occupies space, has weight, and has inertia.

8 More Clarification Mass depends upon the amount of matter remains the same regardless of where the object is located. Weight is not mass. Weight is dependent upon the location from the center of the earth. It is the measure of attraction of the earth for an object.

9 Determining Mass We can determine mass by measuring the mass of an object by comparing it with a known mass or standard. Sometimes we can weigh materials directly Density- weight of a substance per unit volume D=m/v

10 States of Matter Matter may exist as Solid Liquid Gas Matter may change from state to state if adequate energy is added or subtracted from the system.

11 Characteristics of Solids Rigid Definite Shape Non-compressible Definite Volume

12 Characteristics of Liquids Fluid Shape of Container Non-compressible Definite Volume

13 Characteristics of Gases Fluid Indefinite Shape Highly compressible Indefinite Volume

14 What are some important properties of and changes in matter? Properties- characteristics by which substances may be identified There are two types physical which describe appearance Qualitative words: color, odor, taste, crystalline form, and physical state Quantitative: density, hardness, solubility, melting point, and boiling point Chemical which describes chemical behavior

15 Physical vs Chemical Changes Physical Characteristics which can be recognized without changing the nature of the substance Chemical Characteristics which describes how a substance reacts with other substances It is the way that materials behave with other materials Inactive, active, Inert Chemical changes/ reactions are required

16 Changes in Matter If you tear a piece of paper. Physical If you burn a piece of paper Chemical A current of electricity passing through water Chemical Remember physical does not alter the chemical composition, only a chemical change alters the chemical composition

17 Energy Energy is the ability to do work This includes mechanical, chemical, and nuclear Mechanical may be in the form of potential energy (position- non moving) or it can be kinetic energy (moving) Energy can be transferred from one place to another, body to body, undergo changes in form or kind.

18 Here is the connection between matter and energy! All matter possess energy in some form or another! A characteristic of chemical change and many kinds of physical changes is a change in energy content.

19 Two types of Reactions Chemical Reactions Exothermic- give off heat energy Endothermic-absorbs heat energy

20 One step further on the Connection. Energy and matter are further connected by the law of conservation Energy can neither be created nor destroyed, but only changed in matter Matter may neither be created nor destroyed, but only changed in forms One exception: nuclear energy- some matter is actually lost and is changed completely into energy. Einstein made the connection E=mc 2

21 Tah Dah! The law of conservation of energy and mass Matter and energy can neither be created nor destroyed, but can be transformed one into the other That s a law! It is a general statement which summarizes a number of facts It takes place under a given set of conditions They are discovered through observations and experiments

22 Method of Science Lavosier is created with the rise of modern chemistry because he discovered the true nature of burning or combustion. Up to his discovery combustion was thought to occur by an invisible gas called phlogiston theory and no other explanation was given.

23 More on Lavoisier Lavosier took Joseph Preistley s, another scientist, experiment with heated mercury. Lavosier used sealed flasks and measured out the mercury. He heated the mercury in a closed flask thus a closed system. After wards he measured the gas that was given off in the bell jar.

24 More on Lavosier What did he find? He found that the gas constituted one-fifth of the air and he named it oxygen. He also weighed the mass of the ash and conclude that oxygen had combined with mercury and formed an oxide. He also concluded that mass had neither been created nor destroyed.

25 Why was he successful? He used experimental methods of science, which involved exact measurements of the quantities of substance used. This procedure enabled him to draw the correct conclusion rather than myths and guess work.

26 Scientific Method Observation Hypothesis Experiment Evaluate Results Match Hypothesis Results do not match hypothesis Conclude Return to Hypothesis step Reformulate Hypothesis and Retest

27 True Scientific Thinking Is a willingness to let evidence determine judgement It tries to rule out subjective influences and depends on only reproducible observations and measurements. It also tries to distinguish between facts and theories Facts are observable phenomena Theories are merely good guesses about things that cannot be proven through direct observations.