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Chapter 1: Keys to the Study of Chemistry
Transcript of Chapter 1: Keys to the Study of Chemistry
The study of matter and its properties, the changes that matter undergoes, and the energy associated with those changes. Chapter One SI Units: Chemistry Matter:
the stuff of the universe: air, glass, planets, students--anything that has mass and volume.
anything that posses mass and occupies volume.
we learn about matter by observing its properties.
Matter occurs commonly in three physical forms called states: solid, liquid, gas. Composition: (of matter) the types and amount of simpler substances that make it up.
a substance is a type of matter that has a defined, fixed composition.
Composition ultimately depends on the makeup of substances at the atomic scale (similarly, macroscopic properties of substances in any of the three states arise from atomic-scale behavior of their particles). Substance: a type of matter either an element or compound, that has a fixed composition.
to identify a substance, we observe two types of properties, physical and chemical, which are loosely related to two types of change that matter undergoes. Properties: the characteristics that give each substance it's unique identity. Physical Properties: characteristics that shows by itself without changing or interacting with another substance.
EX: melting point, electrical conductivity, and density. Physical Change: occurs when a substance alters its physical properties, not its composition.
EX: ice melting: what changes is the hardness, density, and gains the ability to flow. Except the composition did not change (still water)
a change in which the physical form (or state) of a substance, but not its composition, is altered. Chemical Properties: characteristics that a substance shows as it changes into or interacts with another substance (or substances).
EX: flammability, corrosiveness, and reactivity with acids. Chemical Change: occurs when a substance converted into a different substance (or substances).
also known as a chemical reaction.
A change in which one or more substances are converted into one or more substances with different composition and properties.\
EX: passing an electric current through water: the water decomposes (break down) into two other substances, hydrogen and oxygen, that bubble into the tubes. The composition has changed: the final sample is no longer water!
Refer back to pages 5 through 6. States Liquid: Solid: has a fixed shape that does not conform to the container shape.
solids are not defined by rigidity or hardness: solid iron is rigid and hard, but solid lead is flexible, and solid wax is soft.
One of the three states of matter.
a solid has a fixed shape that does not conform to the container shape.
in a solid, the particles lie next to each other in a regular, three-dimensional array. has a varying shape that conforms to the container shape, but only to the extent of the liquid's volume; that is, a liquid has an upper surface.
one of the three states of matter.
a liquid fills a container to the extent of its own volume and thus forms a surface.
in a liquid, the particles also lie close together but move randomly around each other. Gas: has a varying shape that conforms to the container shape, but it fills the entire container and, thus, does not have a surface.
one of the three states of matter.
a gas fills its container regardless of the shape because its particles are far apart.
(In a gas, the particles have large distances between them and move randomly throughout the container.) refer to page 6 for figure 1.2 for image of states Effect of temperature on States depending on the temperature and pressure of the surroundings, many substances can exist in each of the three physical states and undergo changes in states as well.
The main point is that a physical change caused by heating can generally be reversed by cooling (this is not generally true for a chemical change).
EX: melting or freezing ice v.s. the chemical change in iron. The Central Theme in Chemistry Understanding the properties of a substance and the changes it undergoes leads to the central theme in chemistry: macroscopic-scale properties and behavior, those we can see, are the results of atomic-scale properties and behavior that we cannot see. The distinction between chemical and physical change is defined by composition, which we study macroscopically. Central Idea We study observable changes in matter to understand their unobservable causes. The Importance of Energy
in the Study of Matter physical and chemical changes are accompanied by energy changes. Energy: often defined as the ability to do work.
the capacity to do work, that is, to move matter.
all work involves moving something.
the object doing the work (arm, engine, rock) transfers some of the energy it possesses to the object on which the work is done (book, wheels, ground). Potential Energy: the energy due to the position of the object relative to other objects.
the energy an object has as a result of its position relative to other objects or because of its composition. Kinetic Energy: the energy due to the motion of the object.
the energy an object has because of its motion. Two concepts central to all cases involving energy: when energy is converted from one form to the other (potential/kinetic energy), it is conserved, not destroyed.
situations of lower energy are more stable, and therefore favored, over situations of higher energy (less stable). refer back to page 8! Refer back to page 9 for Summary of 1.1! Conversion Factors: ratios used to express a quantity in different units.
a ratio of equivalent quantities that is equal to 1 and used to convert the units of a quantity.
remember to check on moodle what units I need to know for conversion.
refer to page 15 for systematic approach to solving chemistry problems.
refer to page 16 for summary of 1.4! Measurement in Scientific Study a unit composed of one or more of the base units of the Systeme International d'Unites (in french), a revised metric system.
created by a committee in France who revised the metric system and established this universally accepted unit. the sI system is based on seven fundamental units or base units. Base Units: A unit that defines the standard for one of the seven physical quantities in the International system of Units (SI).
each identified with a physical quantity (mass, length, time v.s. kliogram, meter, second). other units are derived units. Derived units: combinations of the seven base units
derived units that are a ratio of base units can be used as conversion factors
EX: the derived unit for speed. for quantities much smaller or larger than the base unit, we use decimal prefixed and exponential (scientific) notation. (refer to page 17, table 1.3). refer o page 17, table 1.2 table 1.4 on page 17 shows some SI quantities for length, volume, and mass with their English-system. the SI base unit of length is meter (m).
the SI unit of volume is cubic meter.
often use non-SI units like liter and milliliters. Mass: the quantity of matter an object contains.
SI unit of mass is the kilogram (kg).
balances are designed to measure mass. the terms mass and weight have distinct meanings: mass is constant because an object's quantity of matter cannot change.
weight is variable because it depends on the local gravitational field acting on the object. Weight: the force exerted by a gravitational field on an object that is directly proportional to its mass.
because the strength of the gravitational field varies with altitude, you (and other objects) weigh slightly less on a high mountain than at sea level. Density (d): the density is its mass divided by its volume.
An intensive physical property of a substance at a given temperature and pressure, defined as the ratio of the mass to the volume (d = m/V). Temperature v.s. Heat is a measure of how hot or cold one object is relative to another.
a measure of how hot or cold a substance is relative to another substance.
a measure of the average kinetic energy of the particles in a sample.
in the lab, we measure temperature with a thermometer.
three temperature scales: the Celsius (degree with C), the Kelvin (K), and the Fahrenheit (degree with F).
the SI base unit of temperature is the kelvin (the kelvin is the same size as the Celsius degree--the kelvin scale uses the same size degree as the Celsius scale 1/100 of the difference between the freezing and boiling points of water
in the Kelvin scale, all temperatures are positive. Temperature (T): Heat: (also thermal energy) the energy transferred between objects because of a difference in their temperatures only. know how to convert the different temperature scales. Second (s):
is now based on atomic standard.
chemist now lasers to measure the speed of extremely fast reactions that occur. Extensive Properties: some variables are dependent on the amount of substance present; these are called extensive properties.
EX: mass, volume, and heat (energy) Intensive Properties: intensive properties are independent of the amount of substance.
EX: density and temperature EX for both situations: a gallon of water has four times the mass of a quart of water, but it also has hour times the volume, so the density, the ratio of mass to volume, is the same for both samples.
EX 2: a vat of boiling water has more heat, more energy, than a cup of boiling water, but both samples have the same temperature. refer to page 25 for 1.5 summary! Determining which Digits are Significant all digits are significant, except zeros used only to position the decimal point. a complication can arise when zeros end a number: the following procedure applies this point:
1. make sure the measurement has a decimal point.
2. start at the left, and move right until you reach the first nonzero digit.
3. count that digit and every digit to its right as significant. if there is a decimal point and the zeros lie either after or before it, they are significant: 1.1300 (5 s.f.) and 6500. (4 s.f.)
if there is no decimal point, we assume that the zeros are not significant, unless exponential notation clarifies the quantity
a terminal decimal point indicates that zeros are significant: 500 v.s 500. and 0.500 Significant Figure: Calculations and Rounding Off the general rule for rounding is that the least certain measurement sets the limit on certainty for the entire calculation and determines the number of s.f. in the final answer. Rules for Arithmetic Operation: 1. for multiplication and division: the answer contains the same number of s.f. as there are in the measurement with the fewest s.f.
2. for addition and subtraction: the answer has the same number of decimal places as there are in the measurement with the fewest decimal places. Rules for Rounding Off: 1. if the digit removed is more than 5, the preceding number increases by 1: 5.379 rounds 5.38 if you need three s.f. and to 5.4 if you need two.
2. if the digit removed is less than 5, the preceding number remain the same: 0.2413 rounds to 0.241 if you need three s.f. and to 0.24 if you need two.
3. if the digit removed is 5, the preceding number increases by one if it is odd and remains the same if it is even: 17.75 rounds to 17.8, but 17.65 rounds to 17.6. If the 5 is followed only be zeros, rule 3 is followed; if the 5 is followed by nonzeros, rule 1 is followed: 17.6500 rounds to 17.6, but 17.6513 rounds to 17.7. Significant Figures: the digits we record, both the certain and the uncertain ones are called s.f.the digits obtained in a measurement.
the greater the number of s.f., the greater the certainty of the measurement. Precision: (reproducibility) refers to how close the measurements in a series are to each other
the closeness of a measurement to other measurements of the same phenomenon in a series of experiments. Accuracy: refers to how close each measurements is to the actual value.
the closeness of a measurement to the actual value. Systematic Error: produces values that either all higher OR all lower than the actual value.
this type of error is part of the experimental system, often cause by a faulty device or by a consistent mistake in taking a reading.
a type of error producing values that are all either higher or lower than the actual value, often caused by faultly equipment or a consistent flaw in technique. Random Error: in the absence of systematic error, it produces values that are higher AND lower than the actual value.
Random errors always occurs, but its size depends on the measurer's skill and the instrument's precision. Precision, Accuracy, and Instrumental Calibration Precise measurements have low random errors, that is, small deviations from the average.
Accurate measurements have low systematic error and, generally, low random error.
In some cases, when many measurements have a high random error, the average may still be accurate. Calibration: systematic errors can be taken into account through calibration, comparing the measuring device with a known standard.
the process of correcting for systematic error of a measuring device by comparing it to a known standard. refer to page 29 for 1.6 summary!