Our primary interest in chemistry is how matter can change and the energies associated with that change. To begin this investigation, we must understand matter itself.

MATTER:

• anything that has mass and occupies space

• it can be a single chemical substance or a complex mixture of substances

STATES of Matter:

• solid
• solids have a definite shape and volume such as an ice cube which stands alone with its own volume and shape.
• particles which make up matter (to be defined soon) are closest together in the solid state, have the least amount of energy associated with them and move the slowest.
• particles have the greatest attractive forces between them in the solid state (we will learn more about attractive forces in chapter 12).
• liquid
• liquids have an indefinite shape but a definite volume such as a glass of water which assumes the shape of its container but does not assume the volume of the container.
• particles which make up matter in the liquid state are farther apart, have a lesser amount of energy associated with them and move faster than in the solid state.
• particles have smaller attractive forces between them in the liquid state.
• gas
• gases have both indefinite shape and volume such as air which will assume the shape and volume of the container in which it resides.
• particles which make up matter in the gaseous state are the farthest apart, have the greatest amount of energy associated with them and move the fastest.
• particles have the smallest attractive forces between them in the gaseous state.
  

 Changes of State:

Matter can undergo a change of state with a concurrent energy change.  Let’s look at the terms which are associated with a change of state of matter:

• melting and freezing are the terms which define a change in state between liquid and solid
• the melting point/freezing point is the temperature at which this change occurs

• boiling and condensation are the terms which define a change in state between liquid and gas
• the boiling point/condensation point is the temperature at which this change occurs
• because any change which involves the gaseous state will depend upon the pressure of the system, we define the normal boiling point as the temperature at which a liquid boils under normal atmospheric pressure (we will study the concept of gases and boiling points more thoroughly in chapter 11) 

All matter can be identified by a set of specific properties which it exhibits.  Physical properties and chemical properties (and the changes that are associated with them) are just some of the properties which aid in the identification of matter.

• Physical property is a characteristic of matter which can be observed without changing the chemical identity of the matter
• such as the boiling point of water, which indicates a change of state but not a change in the chemical identity of the matter
• Chemical property is a characteristic of matter which involves the chemical change of matter
• such as the blackened crust which occurs in the burning of toast, it indicates a chemical change has occurred to the toast
• Physical change is a change of form of matter but not chemical identity of the matter
• such as a change of state from liquid to solid—the matter is the same, the state is different
• Chemical change occurs when one or more kinds of matter is transformed into one or more different kinds of matter
• such as the change of two individual substances, oxygen and hydrogen, into a very different substance, water

Let’s look at more definitions which will help us understand matter:

• PURE SUBSTANCE is a substance with constant composition, a fixed set of chemical and physical properties, and cannot be separated by a physical process into simpler substances
  
• water is an example of a pure substance—although it is composed of two substances (hydrogen and oxygen), if it is separated into those two substances it is no longer water, it is chemically different—in other words, the separation was chemical in nature, not physical.

• MIXTURE is composed of two or more pure substances, can vary in composition and the properties will be different for different compositions. Mixtures can be separated into their components by a physical process. There are two types of mixtures:

• Homogeneous has a uniform appearance and same properties throughout the mixture – a homogeneous mixture is commonly called a solution

• Heterogeneous consists of physically distinct parts with different properties and has a non-uniform appearance and variable properties.

• SEPARATION of Mixtures
• filtration
• the process of separating a liquid from a suspended solid (commonly called a precipitate) much like the preparation of coffee if you use the filter method.
• distillation
• the process of separating two substances which have different boiling temperatures. The lower boiling substance vaporizes first an exits the container leaving the other component in liquid form. The vaporized substance is then collected by condensing it into a separate container.

How can we determine whether a property or change is chemical or physical unless we know something about the composition of matter--what is it composed of and how it can change?

• ELEMENT – a pure substance that cannot be decomposed by chemical means into a simpler substance. Elements are the basis of all matter and can be combined chemically to produce compounds.
• All elements have names with either one- or two-letter abbreviated symbols. Many names are derived from Greek or Latin terms. For example:

The Periodic Table gives all the elements, their symbols and much more useful information of which we will learn soon. The abbreviated Periodic Table below shows all the elemental symbols in their respective positions (those positions will be very important later).

• ATOM – the smallest particle of an element which can be identified as that element, atoms are the limit of chemical subdivision for matter

• COMPOUND – a pure substance composed of two or more elements which are chemically combined -- a chemcal combination of elements
  
• a compound cannot be physically separated or divided (it can be chemically separated into its individual elements, but then it would no longer be the original substance--it would be different, changed and no longer have the same properties)

• MOLECULE – the smallest particle of a compound which can be identified as that compound and is capable of a stable independent existence -- a chemcal combination of atoms

• a molecule cannot be physically separated or divided (it can be chemically separated into its individual atoms, but then it would no longer be the original substance--it would be different, changed and no longer have the same properties)

A compound has a given, definite composition which always occurs for that compound –

• LAW OF DEFINITE (OR CONSTANT) COMPOSITION: a compound, no matter what its source, always contains definite, or constant, proportions of its elements by mass
• for example, 1.000 g of water (no matter what the source) will always contain 0.889 g of oxygen and 0.111 g of hydrogen

• LAW OF CONSERVATION OF MASS: total mass remains constant during a chemical reaction
• for example, even though a nail appears to gain mass when it rusts, when you consider the complete reaction, the mass of all the reactants equals the mass of all products
  
  iron        plus       oxygen    goes to    rusted iron nail
  4Fe       +           3O₂       ®           2Fe₂O₃

                    223 g            +            96 g                =             319 g

• ENERGY -- by nature, energy is a more abstract concept than matter—it is defined as the potential or capacity to move matter

• kinetic energy – is the energy of motion – anything that moves has kinetic energy
• potential energy – is the energy of position – everything which has the potential to move has potential energy
• chemical energy is a form potential energy—chemical reactions can produce energy which can perform work due to the makeup of and changes which occur to the elements involved in the chemicals that react
• units of energy—the SI unit of energy is the joule and is used primarily in the sciences, however, the calorie is an older unit which is still used. The food unit, Calorie, is actually one kilocalorie or 1000 calories.
  
  1 joule (J) = 1 kg m² /s²
  
  1 calorie (cal)   =   4.184 joules      and is defined as the quantity of energy needed to raise the
                                                             temperature of 1g of water by 1° C

• SPECIFIC HEAT: all substances have a property known as specific heat which is defined as the quantity of heat energy required to raise the temperature of 1 g of a substance by 1° C we use specific heat to determine the relationship between energy and temperature change, more specifically (no pun intended!), if a reaction causes the temperature of a substance to increase (or decrease), we can determine the amount of energy that the reaction produced (or used), if we know the specific heat of the substance.
  
• LAW OF CONSERVATION OF ENERGY: energy may be converted from one form to another, but the total quantity of energy remains constant in the universe

Sample Problems:

• Convert 5.23 J to calories and to Calories.
• we need conversion factors:    4.184 J  =  1 cal   &     10³ cal = 1 Cal
  therefore, 4.184 x 10³ J   =   1 Cal
  
  5.23 J x 1 cal    =    1.25 cal     &     1.25 cal x 1 Cal    =     1.25 x 10 ^–3 Cal
             4.184 J                                                      10³ cal
  
  
• When a sample of platinum weighing 8.75 g has 5.68 J of heat added to it, the temperature rises from 25.47°C to 30.35°C. What is the specific heat of platinum according to these data?
• the units of specific heat are     J    where °C is DT (T_final - T_initial) or 30.35°C – 25.47°C = 4.88°C
                                                     g°C
  
        5.68 J                =    0.133 J
  (8.75 g)(4.88°C)                      g°C
  
  
• A chunk of lead at 26°C and weighing 42 g is placed in a beaker of 100 g of boiling water at 100°C. How much heat has passed into the lead by the time its temperature becomes equal to that of the boiling water? The specific heat of lead is 0.129 J/g °C and that of water is 4.184 J/g °C.
• we need conversion factors:         0.129 J   =   1 g °C    &     4.184 J   =   1 g °C
  and a pattern:           heat gained by lead  =  - heat lost by the water
  heat gained by lead  =  (sp. ht   x   g   x   DT)_lead [DT = T_final – T_initial]
  heat lost by water  =   (sp. ht. x g x DT)_water
  
  0.129 J    x     42 g    x     (T_f - 26)°C     =     - 4.184 J    x    100 g    x    (100 - T_f )°C
     g °C                                                                  g °C
  
  5.418 J    x    (T_f - 26)°C    =    - 418.4 J    x    (T_f – 100)°C        solve for T_f
        °C                                                °C
  
  (5.418 T_f) J    -  140.87 J     =    - (418.4 T_f) J    +    4.184 x 10⁴ J
  
  (423.82 T_f) J   =    4.1981 x 10⁴ J
  
  T_f = 99 °C the amount of energy absorbed by the lead about 4.0 x 10² J
  
  pay attention to significant figures!
  
• The light produced in old camera flash bulbs was produced by burning magnesium, Mg. If the mass of the magnesium in a flash bulb is 2.3 g and the mass of the residue after the flash (magnesium oxide or MgO) is 3.8 g how many grams of oxygen was used in the reaction?
• the reaction is         magnesium    +     oxygen     ®     magnesium oxide
                                           2.3 g                       ? g                               3.8 g
  
  we know that the sum of the mass of all reactants must equal the sum of the mass of all products, therefore the mass of oxygen is 1.5 g
  
• the actual balanced chemical equation is:         2Mg + O₂ ® 2MgO
  we will learn about chemical equations and how to write and balance them in chapter 6