Chemistry Notes

Chapter 1: Chemistry and Scientific Method

Important Concepts

• Anything boxed, underlined, or bracketed is important.

1.2 Scientific Method

• Definition of Science: Science is one way of seeking principles of order in the natural world.
• Definition of Chemistry: Chemistry is the science that deals with the materials of the universe and the changes that these materials undergo.

Scientific Method Steps

• A. Making observations
• B. Formulating Hypotheses
• C. Performing Experiments

Theory vs. Law

• A law summarizes what happens in nature.
• A theory explains why it happens.

1.6 Dimensional Analysis

• Dimensional analysis: Using conversion factors to change from one unit to another.
• Equivalence statement: One amount is equal to another amount.
• Conversion factor: One amount over (divided by) another amount equals one.

Basic Steps to Dimensional Analysis

1. WRITE WHAT YOU KNOW
2. TIMES AND DRAW A LINE
   • A. Put the unit you already have on the bottom (so that it cancels out).
   • B. Put the unit that you need to get on the top
     • a. Write the labels
     • b. Repeat as many times as you need
3. Sigfigs ☠

• It’s often helpful to write out a little “roadmap” if you’re doing multiple dimensional analyses.
  • Ex: grams -> kilograms -> pounds
• ALWAYS write your calculations in one line instead of breaking it into several calculations
• Labels will cancel out

1.7 Temperature

• Daniel Fahrenheit
  • Made the Fahrenheit scale.
  • Freezing point of water is $32$ degrees, boiling point of water is $212$ degrees.
• Anders Celsius
  • Created the Celsius scale.
  • Freezing point of water is $0$ degrees, boiling point of water is $100$ degrees.
• William Thompson (Lord Kelvin)
  • Made the Kelvin scale.
  • Kelvin scale is Celsius scale plus $273$ degrees.

Temperature Conversions

• $K = C + 273$
• $F = 1.8 * C + 32$
• $C = (F - 32) / 1.8$

1.8 Density

• Density is a property of matter that measures the mass of a substance per unit of volume of the substance.
• $Density = \frac{Mass}{Volume}$
• Don’t do sigfigs till the final answer
• *Don’t forget to do sigfigs before you change operations. Look at the number they give you.
• Remember sigfigs!!
• Convert to grams and centimeters first

1.9 Classification of Matter and Physical/Chemical Changes

Matter

• MATTER is anything that takes up space (VOLUME) and weighs something (MASS)

States of Matter

• Bose-Einstein Condensate (BEC)
• Solid: rigid, has fixed volume and shape
• Liquid: definite volume but no definite shape
• Gas: no fixed volume and shape; takes on the shape and volume of its container
• Plasma

Classification

• Element: Any substance that cannot be broken down into simpler substances
• Compound: A substance with constant composition (made up of only one type of thing) that can be broken down into elements by chemical processes.
• Pure substance: A substance with constant composition (made up of only one type of compound or element)
• Mixture: Matter that has variable composition (made up of two or more different things)
  • Heterogeneous: Having visibly distinguishable parts (can identify the different parts)
  • Homogeneous: Having visibly indistinguishable parts (looks like only one thing)
  • Solution: A homogeneous mixture

Physical and Chemical Changes

• Physical change: A change in the form of a substance, not in its chemical composition.

  • A physical change can be used to separate a mixture into pure compounds, but it will not break compounds into elements.

• Chemical change: A change in which a given substance becomes a new substance or substances with different properties and different composition.

  • Basically, physical changes only change HOW the substance is (ex: changing state of matter, separating a mixture into pure substances) while chemical changes change WHAT the substance is (ex: electrolysis, which is splitting a water atom into hydrogen and oxygen)

• One way of thinking of it:

  • Physical changes change things in the way you expect
  • Chemical changes change things in unexpected ways