The Foundations of Chemistry: Matter,Energy, and Measurements

Página 1

Chemistry

the study of matter and the changes that matter undergoes

Matter

anything that has mass and occupies space

made of small building blocks called atoms

atoms combine to form molecules

molecules can be represented in molecular formulas and models

An example of a molecular model is a "ball-and-stick". each element is represented by a particular color

States of Matter

Gas: compressible and assumes the shape & volume of its container

Liquid: not compressible;will assume the shape of container; has definite volume

Solid: not compressible; has a fixed shape and volume

Classification of Matter

Substance or Mixture

Substance can be either an element or a compound

has a definite composition and distinct properties

EX Sodium chloride, water, oxygen

Element: cannot be seperated chemically

EX: iron, mercury, oxygen

Compounds: two or more elements chemically combined in definite ratios; cannot be separated physically

EX: Salt , water, CO2

Mixture: physical combination of two or more substances that have distinct identities; can be separated physically

There are two types of mixtures; homogenous and heterogenous

Homogenous: composition of mixture is uniform throughout

ex: sugar dissolved in water

Heterogenous: composition of mixture is not uniform

ex: sugar mixed with iron fillings

Filtration: a way to separate mixtures

A mixture of a solid and a liquid is poured into a porous medium like a filter paper. The liquid passes through the paper while the solid remains on the paper.

Distillation: used to separate sodium chloride solutions

The solution is boiled; the water evaporates and is condensed and collected in a receiving flask. The salt is left at the bottom of the boiling flask

Chromatography: ink components are separated during this test

water begins to move up the paper and passes ink spots; the ink spots dissolve at different rates leaving spots on the paper

Comprehension Check

Aluminum foil

element

Baking Soda

compound

Milk

Homogenous

Copper Wire

element

Air

homogenous

Hot fudge sundae

heterogenous

Shampoo

homogenous

Sugar water

homogenous

Peach pie

heterogenous

Properties of Matter

Physical Property

determine without changing the identity of the substance

Physical change

matter undergoes a change at the macroscopic level, but no change in composition

Chemical Property

undergoes a change in composition and the way a substance can change or react to form other substances

Chemical Change: matter undergoes a change in composition/structure

Conservation of Mass

There is no new matter

matter is neither created nor destroyed in a chemical reaction

in a nuclear reaction significant changes in mass occur

during physical and chemical changes the total amount of matter remains costant

Energy

the capacity to do work

Work: result of force acting on a distance

Law of Conservation of Energy: no matter is created or destroyed; total amount of energy is constant

Energy can be changed from one form to another; transferred to one object to another

Kinetic energy: the energy associated with its motion

Potential energy: the energy associated with its position or composition

Electrical energy: energy associated with the flow of electrical charge

Thermal energy: energy associated with random motion of atoms and molecules

Chemical energy: a form of potential energy associated with the position of particles that compose the chemical system

Units of Energy

Joule(J): the SI unit of energy; named after english scientist James Joule

Calorie(cal): the amount of energy required to raise the temperature of 1 gram of water by 1 degree Celsius; 1 calorie=4.184 J

Calorie (Cal): nutritional calorie; 1 Cal= 1000 calories

Kilowatt(kWh)=3.60x10^6 J

Exothermic reactions: energy is released

Endothermic reaction: energy is absorbed

Temperature

the atoms and molecules that are in constant motion give off thermal energy

Temperature: measures the thermal energy of a substance

Heat: the transfer/exchange of thermal energy caused by temperature difference

Fahrenheit: water freezes at 32 degrees; boils at 212 degrees

Celsius: water freezes at 0 degrees; boils at 22 degrees

Kelvin: no negative temperatures; coldest temp is 0K

Heat Capacity: the quantity of heat in joules required to change the temperature of a given amount of substance by 1 degree C

Specific heat capacity: when the amount of the substance is expressed in grams and has units of joules per gram per degree celsius: J/g degrees C

Energy and Heat Capacity Equations

q is the amount of heat in joules

m is the mass of a substance in gram s

C is the specific heat capacity in joules per gram per degrees C

T is the temperatre change in C

the triangle symbol means the “the change in”

Scientific Method

Hypothesis: prediction concerning a phenomenon/educated guess which can be tested

Experiment: hypothesis is tested

Data: facts from the observation and measurements

Scientific Laws: summary of patterns in brief statements

Theory: explanation of the observations and the predications can be tested

Scientific Measurements

The metric system or SI (international system) is

a decimal system based on 10

used in most of the world

used everywhere by scientists

Units in the Metric System

Measurement Metric SI

Length meter(m) meter(m)

Volume liter(L) cubic meter(m^3)

Mass gram(g) kilogram(kg)

Time second(s) second(s)

Temperature Celsius(C) Kelvin(K)

Comprehension Check

A bag of tomatoes is 4.6kg

mass

A person is 2.0 m tall

length

A medication contains 0.50g of aspirin

mass

A bottle contains 1.5L of water

volume

Temperature Conversion

Tc= Tf - 32/1.8

Tf= 1.8Tc +32

K=C+273.15

Comprehension Check

85C------>F

-12.2C------>F

335F------->C

20.8F------->C

Uncertainty in Measurements

Exact: numbers with defined values

Inexact: numbers obtained from any other method other than counting

Inexact beacause of inaccurately calibrated instruments, human error etc.

There are two ways to gauge the quality of a set of measure numbers:

Precision: measure of how closely individual measurements agree with each other

Accuracy: how closely individually measured numbers agree with the correct or true value

Significant Figures

use to conveny uncertainty

non zero digits are always significant; 1 2 3 etc.

Zeros between nonzero digits are always significant; 1005

Zeros at the beginning of a number are NEVER significant. they are place holders; 0.02 1 sig fig

Zeros that fall at the end of a number and after the decimal point are always significant; 0.200g has 3 sig figs. 2.0 has 2 sig figs

When a number ends in zeros but contains no decimal point, the zeros are not significant; 130 2 sig figs 10300 3 sig figs

Comprehension Check

How many sig figs in the following numbers?

7.001

4

0.0107

3

Multiplication and Division

the same number of sig figs as the measurement with the fewest sig figs must be used

use rounding rules to obtain the correct number of sig figs

Addition and Subtraction

use the same number of decimal places as the measurement with the fewest decimal places

use rounding rules to adjust the number of digits in the answer

Conversion Factor Method

Equalities

use two different units to describe the same measured amount

are written for relationship between units of the metric system, US units, or between metric and US units

EX: 1m=1000mm

A conversion factor

a fraction obtained from an equality

1in=2.54cm

written as a ratio with numerator/denominator

can be inverted to give two conversion factors for every equality

may be obtained from information in a word problem

Problem Solving: Given and Needed Units

To solve a problem

Identify the GIVEN

Identify the NEEDED

write them down

write a unit plan to convert the given unit to the needed unit

write equalities and conversion factors that connect the units

use conversion factors to cancel the given unit and provide the needed unit

Density

compares the mass of an object to its volume

is the mass of a substance divided by its volume

Density=mass/volume g/ml

Volume by displacement

a solid completely submerged in water displaces its own volume of water

the volume of the solid is calculated from the volume difference

Density as a Conversion Factor

a substance of 3.8 g/ml equates to

3.8g=1ml

MAtter

energy

MEasurements