# Ch. 2 Chemistry

## Terms

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- Scientific method
- a logical approach to solving problems by observing and collecting data, formulating hypotheses, testing hypotheses, and formulating theories that are supported by data
- System
- a specific portion of matter in a given region of space that has been selected for study during an experiment or observation
- Hypothesis
- testable statement (basis for making predictions)
- model
- an explanation of how phenomena occur and how data or events are related
- theory
- a broad generalization that explains a body of facts or phenomena
- quantity
- something that has magnitude, size, or amount
- SI
- Le Systeme International d' Unites-the measurement system accepted worldwide
- weight
- a measure of the gravitational pull on matter
- derived units
- a unit that is a combination of SI base units
- volume
- the amount of space occupied by an object
- density
- the ratio of mass to volume, or mass divided by volume
- accuracy
- refers to the closeness of measurements to the correct or accepted value of the quanity measured
- precision
- refers to the closeness of a set of measurements of the same quantity made in the same way (not close to accepted value)
- percent error
- a value calculated by subtracting the experimental value from the accepted value, divinding the difference by the accepted value, and then multiplying by 100
- significant figures
- a measurement consist of all the digits known with certainty plus one final digit, which is somewhat uncertain or is estimated
- conversion factor
- a ratio derived from the equality between two different units that can be used to convert from one unit to the other
- scientific notation
- numbers are written in the form M x 10n where the factor M is a number greater than or equal to 1 but less than 10 and n is a whole number (exponent)
- directly proportional
- two quantities that give a constant value when one is divided by the other
- inversely proportional
- two quantities that have a constant mathematical product