Homogeneous: - Mixture that is uniform in composition.
Commonly referred to as solution.
Examples include: gasoline, soda pop, salt solution.
Separation of a mixture through physical methods
Separation of a compound through chemical methods
PROPERTIES OF MATTER
Properties are characteristics that give substances their unique identity, and can be used to distinguish one sample from another.
A physical property is one, which a substance displays without changing its composition. Examples: color, melting point, density, electrical conductivity
A chemical property is one, which a substance displays as it interacts with, or transforms into other substances (changes its composition). Examples: flammability, corrosiveness, reactivity with acids.
A physical change is change in physical properties of matter without change in composition. Physical changes are reversible. Examples: melting of ice, formation of dew.
A chemical change (or chemical reaction) is a change that creates new matter. Chemical changes are not easily reversible. Examples: burning of paper, cooking of food, corrosion of metals.
Examples:
Identify each of the following properties as physical or chemical:
a) Oxygen is a gas
b) Helium is un-reactive
c) Water has high specific heat
d) Gasoline is flammable
e) Sodium is soft & shiny
Identify each of the following changes as physical or chemical:
a) Cooking food
b) Mixing sugar in tea
c) Carving wood
d) Burning gas
e) Food molding
CONSERVATION OF MASS
The most fundamental chemical observation of the century was the law of conservation of mass:
Matter is neither created nor destroyed in a chemical reaction.
The number of substances and their properties may change, but the total amount of matter remains constant.
Antoine Lavoisier first proposed the law of conservation of mass after performing careful experiments with closed systems such as that shown below.
ENERGY & HEAT
Energy is defined as the capacity of matter to do work.
There are two types of energy:
Potential (stored) and Kinetic (moving)
Energy possesses many forms (chemical, electrical, thermal, etc.), and can be converted from one form into another.
In chemistry, energy is commonly expressed as heat.
Heat is measured in SI units of joule or the common unit of calorie. (1 cal=4.184 J)
A related energy unit is the nutritional Calorie which is equivalent to 1000 calories (or 1 kcal ).
Residential energy use is measured units of kilowatt-hour (kWh).
TABLE 3.2 Energy Conversion Factors
1 calorie (cal)
4.184 joules (J)
1 Calorie (Cal)
1000 calories
1 kilowatt-
hour (kWh)
joules (J)
Examples:
A candy bar contains 225 Cal of nutritional energy. How many joules does it contain?
ENERGY IN PHYSICAL & CHEMICAL CHANGES
In all physical & chemical changes, matter either absorbs or releases energy.
Higher energy systems are less stable than lower energy systems.
When energy is released during a change, it is said to be exothermic.
When energy is gained during a change, it is said to be endothermic.
(a)
TEMPERATURE & HEAT
Temperature of a substance is the measure of its thermal energy.
The hotter an object, the greater the random motion of its particles, and the higher its temperature.
Heat is the transfer or exchange of thermal energy caused by a temperature difference.
Heat vs. Temperature:
Heat and temperature are not the same thing. Heat energy is the total kinetic energy of the particles of a substance, while temperature is the average kinetic energy of the particles of a substance.
As an analogy, consider the test scores in a class, with points being analogous to heat. In this analogy, heat is like the total number of points, while temperature is the average score.
Test
Score
Test 1
100
Test 2
50
Test 3
100
Test 4
50
Total pts.
300
Avg. pts.
75
Although the same amount of heat is added to both containers, the temperature increases more in the container with the smaller amount of water.
TEMPERATURE SCALES
Thermometer is an instrument that measures temperature and is based on thermometric properties (i.e. expansion of solids or liquids, color change, etc.) of matter.
Three scales are used for measuring temperature:
Fahrenheit (32-212)
Celsius ( 0-100)
Kelvin (absolute) (273-373)
To convert from one scale to another, the following relationships can be used:
or alternately,
Examples:
The melting point of silver is . Convert to Kelvin.
Pure iron melts at about 1800 K . What is this temperature in ?
On a winter day the temperature is outside. What is this temperature on the Celsius scale?
To make ice cream, rock salt is added to crushed ice to reach a temperature of . What is this temperature in Fahrenheit?
QUANTITY OF HEAT
Different materials have different capacities for storing heat.
The specific heat of a substance is the amount of heat required to change the temperature of of that substance by .
The amount of heat lost or gained by a system is determined by the following equation:
The filling of hot apple pie may be too hot to eat, whereas the crust is not.
Shown below are the specific heat of some common substances:
Substance
Aluminum
0.214
0.897
Copper
0.0920
0.385
Iron
0.0308
0.129
Ammonia
0.488
2.04
Ethanol
0.588
2.46
Water
1.00
4.184
Specific Heat & Temperature Change:
When heated, substances with low specific heat have greater increase in temperature than those with high specific heat.
When cooled, substances with low specific heat get have greater decrease in temperature than those with high specific heat.
Specific heat and change in temperature are inversely proportional
Examples:
Determine the amount of heat needed to raise the temperature of 200. g of water by 10.0 . (Specific heat of water is )
Calculate the specific heat of a solid if 1638 J of heat raises the temperature of 125 g of the solid from 25.0 to .
m =
\(\mathrm{C}=\)
\(\Delta \mathrm{T}=\)
\(\mathrm{q}=\)
Ethanol has a specific heat of . When 655 J are added to a sample of ethanol, its temperature rises from to . What is the mass in grams of the ethanol sample?
