an introduction to chemistry. why is chemistry important? used in many professions used to create...
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An introduction to Chemistry
Why is Chemistry Important?• Used in many professions• Used to create new clean sources of energy• Understand and control diseases• Used to help the environment• Improves problem solving skills
Chemistry: an Introduction
Chemistry =A branch of physical science that studies the composition, structure, properties and change of matter.
matter = anything that occupies space and has a mass
ChemistryMost of the phenomena that occur around us involve chemical reactions:• Burning wood or other materials• Rust• Baking• Digestion
Experiment & Explanation
- experiment is the heart of chemistry and chemistry exploration
Experiment = an observation of natural phenomena carried out in a controlled manner so that the results can be duplicated and rational conclusions obtained
Experiment
- must control everything except one variable
- must be able to duplicate results over and over
- change more than one variable = no conclusions can be drawn (NOT an experiment)
Law
Law = a statement that expresses observed behavior
- Tells what happened
Hypothesis
- during research, scientists try to make sense of their observations by devising an explanation - explanations organize thoughts and predict future events - a good hypothesis will suggest other experiments
hypothesis - a tentative explanation of some regularity in nature (NOT AN EDUCATED GUESS)
Theory- if a hypothesis successfully passes MANY tests it becomes known as a theory
Theory = a tested explanation of basic natural phenomena
- cannot be proven absolutely- hold true with the given technology and knowledge
Matter: Physical State
Three States!
1. solids = the form of matter characterized by rigidity; incompressible and has a fixed volume
and shape
Matter: Physical State
2. Liquid = the form of matter that is relatively incompressible fluid; fixed volume no fixed shape
Matter: Physical State
3. gas = the form of matter that is easily compressible fluid; no fixed volume or shape
Matter: Physical State
Elements and Compounds
- before you can define the difference must first look at
a) physical change
b) chemical change
Physical Changephysical change = a change in the form of matter but not in its chemical identityExamples1. change in physical state (solid to liquid)2. dissolving one substance in another3. can be separatedphysical property = a characteristic that can be observed for a material without changing its chemical identity
Chemical ChangeChemical change = a change in which one more more kinds of matter are transformed into a new kinds of matter or several new kinds of matter
Examples: a rusting car, burning a piece of paper…
chemical property = a characteristic of a material involving its chemical change
(ABILITY to react: i.e. the ability for paper to burn
Signs of a chemical change
1. production of an odor
2. change in temperature
3. change in color
4. formation of bubbles
5. formation of a solid (precipitate)
Chemical or Physical?
Practice Problems: 1. burning wood in the back yard
2. tearing a piece of paper in half
3. boiling water until it evaporates
4. melting butter
Law of Conservation of Mass
mass = the quantity of matter in a material - usually measured with a balance
Law of Conservation of Mass = the total mass remains the same during a chemical change; mass cannot be created nor destroyed
Example Problem
You heat 2.53 grams of metallic mercury in air, which produces 2.73 grams of a red-orange residue.
Mercury + air ----> red-orange residue
What is the mass of oxygen that reacts?
Homework!
Conservation of Mass
Worksheet
Homework
Physical versus
Chemical Worksheet
Pure Substance
-Always has the same composition-Either an element or a compound-Unique set of physical properties by which it can be recognized -Cannot be separated by an physical techniques
Mixtures
-One or more substance added together -Can be separated- has variable composition
Two types-Heterogeneous mixture-Homogeneous mixture
Heterogeneous mixtures
heterogeneous mixtures = a mixture that consists of physically distinct parts, each with different properties
Examples:
Homogeneous Mixtures
homogeneous mixture = a mixture that is uniform in its properties throughout a given sample
Examples:
Homogeneous Mixtures
-Known as solutions
-Alloy-Mixture of metals
Your turn!
Homogenous or Heterogeneous?
1) Brass 4) soil
2) chex mix 5) ocean water
3) Chocolate chip cookies 6) kool-aid
Elements
- small number of substances are elements
elements = a substance that cannot be decomposed by any chemical reaction into simpler substances
(118 elements currently- periodic table)
examples: oxygen, nitrogen, sulfur, sodium…
Compounds
compounds = a substance composed of two or more elements chemically combined
i.e. water, carbon dioxide, sodium chloride
-most substances are compounds -unlimited number of compounds can be formed
Your turn!
Element or Compound?
1) nitrogen 4) water
2) Carbon dioxide 5) carbon
3) oxygen 6) sodium chloride
Homework
States of Matter
Worksheet