Unit Four:
Chemical Reactions
Unit Four: Chemical Reactions
Pg. 1
Pg. 2-3
Pg. 4-5
Pg. 6-9
Pg. 10-11
Pg. 12-16
Pg. 16-18
Pg. 19-20
Pg. 21-26
Pg. 27
Pg. 27-28
Pg. 29-32
Pg. 33-34
Phases of Matter
Phase Diagrams
Pressure-temperature diagrams
· Summarizes the effect of temperature and pressure on a substance in a closed container.
· AB line: rate at which solid sublimes to form a gas = rate at which gas condenses to form a solid
§ The points along AB represent all combinations of temperature and pressure at which the solid is in equilibrium with the gas.
· BC line: rate at which liquid boils to form a gas = rate at which gas condenses to form a liquid
· BD line: rate at which solid melts to form a liquid = rate at which liquid freezes to form a solid
§ The BD line is almost vertical because the melting point of a solid is not very sensitive to changes in pressure
· The solid-liquid phase boundary of most substances has a positive slope. This is due to the solid phase having a higher density than the liquid, so that increasing the pressure increases the melting temperature.
Changes in pressure:
§ Point B is the point at which a pure substance can exist simultaneously as a solid, a liquid, and a gas. This is called the triple point.
· Point C is the critical point of the substance, which is the highest temperature and pressure at which a gas and a liquid can coexist
· The “normal” boiling point and freezing point occur at 1 atm pressure.
Temperature vs. Energy Graph:
Melting Point and Freezing Point
· Pure, crystalline solids have a characteristic melting point, the temperature at which the solid melts to become a liquid.
· When the solid is turning into a liquid it remains at a constant temperature until all of the solid becomes a liquid. This is because the energy being put into the solid is going into changing the state of the solid and therefore isn’t used to increase the temperature of the compound. Once all of the solid has become a liquid the temperature can increase.
· Liquids have a characteristic temperature at which they turn into solids, known as their freezing point. In theory, the melting point of a solid should be the same as the freezing point of the liquid.
· Melting points are often used to help identify compounds.
Boiling Point
· When a liquid is heated, it eventually reaches a temperature at which the vapor pressure is large enough that bubbles form inside the body of the liquid. This temperature is called the boiling point. Once the liquid starts to boil, the temperature remains constant until all of the liquid has been converted to a gas.
· Pressure and temperature both affect the freezing and boiling points. Below is a chart that shows the freezing and boiling points of water at 1 atm.
(See Phase Diagram Assign pg 18 & 19)
Solutions
Components of a Solution
· A solution is composed of two or more pure substances, one of which is a solvent and the other a solute.
· A cup of instant coffee is the solution, the hot water is the solvent, and the instant coffee is the solute.
· Solutions in which water is the solvent are called aqueous solutions.
Water as a Solvent
· Most covalent liquids are only able to dissolve other covalent compounds; water can dissolve both ionic and covalent compounds.
The attraction of water dipoles for ions pulls ions out of a crystalline lattice and into aqueous solution.
Solutions:
· A saturated solution is a solution that contains the maximum amount of solute dissolved in a solvent. A supersaturated solution is a solution where conditions have been changed to allow more solute to dissolve than would at room temperature (this is done by heating the solvent or solution).
· When the solvent and solutes are liquids we can use the terms miscible and immiscible. Miscible means that the two liquids will mix together, and immiscible means that the two liquids will not dissolve in one another.
· Sometimes when we mix two dissolved salts together, we end up with a precipitate. This is because a new ionic compound is formed that is insoluble in water.
We can use solubility charts or solubility tables to determine if a solid will be formed.
Solubility Table
Ion / Solubility / ExceptionsNO3– / soluble / none
ClO4– / soluble / none
Cl– / soluble / except Ag+, Hg22+, *Pb2+
I– / soluble / except Ag+, Hg22+, *Pb2+
SO42- / soluble / except Ca2+, Ba2+, Sr2+, Hg2+, Pb2+, Ag+
CO32- / insoluble / except Group IA and NH4+
PO43- / insoluble / except Group IA and NH4+
OH– / insoluble / except Group IA, *Ca2+, Ba2+, Sr2+
S2- / insoluble / except Group IA, IIA and NH4+
Na+ / soluble / none
K+ / soluble / none
NH4+ / soluble / none
* = slightly soluble
Ex. If we mix sodium ions with hydroxide ions will a precipitate form?
No
Ex. If we dissolved sodium hydroxide in calcium chloride, will a precipitate form?
2NaOH + CaCl2 2NaCl + Ca(OH)2
NaCl is soluble, Ca(OH)2 is not soluble so a precipitate will form.
Ex. Calcium nitrate with sodium carbonate
Ca(NO3)2 + Na2CO3 CaCO3 + 2NaNO3
Calcium Carbonate is insoluble so a precipitate will form, sodium nitrate is soluble
Ex. Silver Perchlorate and Calcium Iodide
Ca(ClO4)2 (soluble) and AgI (insoluble)
Examples/Demonstrations
(see Solubility Assign Pg 20)
Chemical Reactions
The Importance of Chemical Reactions
Many chemical reactions occur naturally, although some take place so slowly that we do not notice them.
Biochemical Reactions
The natural chemical reactions that we observe occurring in living things are known as biochemical reactions.
2 important chemical reactions are shown below:
· Respiration: C6H12O6 + 6O2 6CO2 + 6H2O + energy
· Photosynthesis: 12H2O + 6CO2 + energy C6H12O6 + 6H2O + 6O2
Manufacture Important Chemicals
Many important chemicals are created through chemical reactions.
Examples: Fertilizers, cement, plastics, synthetic textiles, and pharmaceuticals.
Harmful Chemical Reactions
There are also chemical reactions that harm living organisms and harm the environment.
(See RAFT assignment)
Review Chemical Reactions:
Indicator that a chemical change has occurred:
· Gas produced
· Solid produced
· Light produced
· Temperature change
· Colour change
· Odour change
Other signs of a chemical change:
· Change in electrical conductivity
· Change in melting point or boiling point
· Change in density
· Change in taste
Types of Chemical Reactions
Chemical Reactions
· A reaction occurs when two or more molecules interact and a chemical change occurs. A chemical change MUST occur in order for a chemical reaction to occur.
· Chemical reactions start with the reactants and go to the products.
Types:
Synthesis/ Combination:
· A synthesis reaction is when two or more simple compounds combine to form a more complicated one. These reactions come in the general form of:
A + B ---> AB
One example of a synthesis reaction is the combination of iron and sulfur to form iron (II) sulfide:
8 Fe + S8 ---> 8 FeS
Decomposition:
· A decomposition reaction is the opposite of a synthesis reaction - a complex molecule breaks down to make simpler ones. These reactions come in the general form:
AB ---> A + B
One example of a decomposition reaction is the electrolysis of water to make oxygen and hydrogen gas:
2 H2O ---> 2 H2 + O2
Single displacement:
· This is when one element trades places with another element in a compound. These reactions come in the general form of:
A + BC ---> AC + B
One example of a single displacement reaction is when magnesium replaces hydrogen in water to make magnesium hydroxide and hydrogen gas:
Mg + 2 H2O ---> Mg(OH)2 + H2
The Activity Series:
The activity series of an element is used to determine whether or not a single displacement reaction will occur.
Each metal will displace any metal ion that appears below it in the series.
The Activity Serieslithium / These metals displace hydrogen from water
potassium
barium
calcium
sodium
magnesium / These metals displace hydrogen from acids
aluminum
zinc
iron
nickel
tin
lead
hydrogen
copper / These metals do not react with acids or pure water
mercury
silver
gold
Examples:
Cu(s) + FeSO4(aq) no reaction
Zn(s) + 2 HCl(aq) ZnCl2(aq) + H2(g)
2 Na(s) + 2 H2O(l) 2 NaOH(aq) + H2(g)
The Halogen Displacement Series
The Halogen Displacement SeriesEach halogen will
displace any halide
ion that appears below it / fluorine
chlorine
bromine
iodine
Examples: determine whether a reaction will occur, if so, what are the products?
Br2(aq) + 2 NaCl(aq)
Zn(s) + NiCl2(aq)
I2(aq) + 2 KF(aq)
F2(aq) + 2 KI(aq)
Cu(s) + 2 AgNO3(aq)
Double displacement:
· This is when the anions and cations of two different molecules switch places, forming two entirely different compounds. These reactions are in the general form:
AB + CD ---> AD + CB
One example of a double displacement reaction is the reaction of lead (II) nitrate with potassium iodide to form lead (II) iodide and potassium nitrate:
Pb(NO3)2 + 2 KI ---> PbI2 + 2 KNO3
How can we predict when a double displacement reaction will occur? Such reactions usually result in the formation of a precipitate, a gas, or water.
Sometimes included as types of reactions:
Acid-base:
· This is a special kind of double displacement reaction that takes place when an acid and base react with each other. The H+ ion in the acid reacts with the OH- ion in the base, causing the formation of water. Generally, the product of this reaction is some ionic salt and water:
HA + BOH ---> H2O + BA
One example of an acid-base reaction is the reaction of hydrobromic acid (HBr) with sodium hydroxide:
HBr + NaOH ---> NaBr + H2O
The base is under a salt: NaCl
NaOH
Combustion:
· A combustion reaction is when oxygen combines with another compound to form water and carbon dioxide. These reactions are exothermic, meaning they produce heat. An example of this kind of reaction is the burning of napthalene:
C10H8 + 12 O2 ---> 10 CO2 + 4 H2O
Steps to determine types of reactions:
Follow this series of questions. When you can answer "yes" to a question, then stop!
1) Does your reaction have oxygen as one of its reactants and carbon dioxide and water as products? If yes, then it's a combustion reaction
2) Does your reaction have two (or more) chemicals combining to form one chemical? If yes, then it's a synthesis reaction
3) Does your reaction have one large molecule falling apart to make several small ones? If yes, then it's a decomposition reaction
4) Does your reaction have any molecules that contain only one element? If yes, then it's a single displacement reaction
5) Does your reaction have water as one of the products? If yes, then it's an acid-base reaction
6) If you haven't answered "yes" to any of the questions above, then you've got a double displacement reaction
Rates of Chemical Reactions
· The rate of reaction is the speed at which reactants combine to form products. Remember that in order for a bond to form a collision must occur. This means that the more collisions the more molecules will bond and the faster the rate will be.
What influences the rate of reaction?
Surface area:
· The greater the surface area of the reactants, the more collisions will occur, and the faster the reaction will take place. So if you increase the surface area of a reactant you will increase the rate of the reaction.
Temperature:
· When the temperature is increased the atoms/molecules move around more so there are more collisions. Because there are more collisions, the rate of the reaction increases. So an increase in temperature results in an increase in the rate of the reaction and vice versa.
Concentration:
· The more molecules or atom you have to combine with another atom or molecule, the greater chance you have of a collision occurring between the molecules. This means there is a greater chance of bonding and therefore an increase in the rate of the reaction. So if you increase the concentration of a reactant, you will increase the rate of the reaction.
Pressure:
· Pressure effects the rate of a reaction but this can be difficult to visualize with a solid or liquid, so think of a gas. The more you increase the pressure, the less area the gas molecules have to move around, so the more likely they are to hit each other. Since an increase in the pressure increases the number of collisions, it also increases the rate of the reaction.
Catalyst:
· A caltalyst is something that is added to the reaction to increase the rate without changing the products. This means that whatever amount of catalyst you put into the reaction, will be the same amount you get out.
· Reactions need a certain amount of energy, in order to occur. If they do not get enough energy, they cannot occur. What a catalyst does is lowers the amount of energy required for the reaction to take place. The energy needed for a reaction to take place is called the activation energy.
· Keep in mind that energy is not matter. In fact energy is anything that is not matter.
Lab 5: Alka-Seltzer Rates of Reaction Lab
Background information:
Today we are going to be observing what occurs when an Alka-seltzer tablet is dissolved in water. An Alka-seltzer tablet produces Carbon dioxide gas when dissolved in water. It is obvious then that the reaction is as follows:
Alka-seltzer + H2O → CO2 + products
However there is a lot more going on than just this simple (looking) reaction.
Alka Seltzer is an effervescent tablet used to relieve pain or an upset stomach. Alka-Seltzer’s primary ingredients are acetylsalicylic acid (aspirin), citric acid (C6H8O7), and sodium bicarbonate (NaHCO3). When the Alka-seltzer is in tablet form, the ingredients of the tablet do not form any sort of reaction, but when dissolved, the citric acid and sodium bicarbonate are able to react.