Unit 4: Chemical Reactions

Question 1

What is a chemical reaction?

Answer 1

It’s a process in which one or more substances change into one or more new substances
- ALL chemical reactions result in the formation of a new compound/substance

Question 2

Clues/indicators that a chemical reaction may have occurred

Answer 2

1) change in colour –> cookie dough baking
2) change in odor when things burn or rot –> eggs rotting
3) New material is created –> combustion of fuel
4) Formation of a precipitate
5) Gas is created –> baking soda reacting with vinegar to form CO2 gas
6) Heat or light is produced
- None of these 6 clues guarantee that a chemical reaction took place

Question 3

The only absolute proof that a chemical reaction has taken place is …..

Answer 3

A new SUBSTANCE is formed.
- the chemical bonds of the initial substances break, and the atoms that compose them separate and rearrange themselves into new substances with new chemical bonds

Question 4

The law of Conservation of Mass

Answer 4

During a chemical reaction, the total mass of reactants equals the total mass of products –> Same number & types of atoms before and after

Question 5

A word equation states….

Answer 5

the names of the reactants and products
Ex. Aluminum + Iron (III) oxide –> Aluminum oxide + Iron

Question 6

A chemical equation states….

Answer 6

the chemical formulas of the reactants and products, their state, and specific conditions required for the reaction to occur
Ex. 2Al(s) + Fe2O3(s) –> Al2O3(s) + 2Fe(l)

Question 7

Is an ionic compound aqueous?

Answer 7

Ionic compounds have a high melting point (>300 degrees).
- So if you have an ionic compound that appears to be in a liquid state @ room temp or @ less than 300 degrees Celsius, it will be an aqueous solution

Question 8

Aqueous state means….

Answer 8

the substance is dissolved in water.

Question 9

Types of Chemical Reactions: combustion reactions (4)

Answer 9

• All fuels burn rapidly with O2 produce CO2, H2O… and a large amount of energy (heat & light)
• These reactions are not spontaneous and must be started by a spark, heat, or light
• Combustion of fossil fuels is a major source of useful energy for humans Ex. natural gas, gasoline, kerosene, candles, wax, jet fuel
• Fuel + O2 –> product + energy

Question 10

Complete combustion reactions (4)

Answer 10

• Occur when the oxygen supply is abundant/not limited. Ex. when you’re outside
• Products: CO2, H2O, & large amounts of energy
• Ideal way to burn a fuel because it releases the greatest amount of energy from the fuel molecules
• produces the cleanest & hottest flames (blue)
  Ex. COMBUSTION OF METHANE
  CH4(g) + 2O2(g) –> CO2(g) + 2H2O(g) + energy

Question 11

Incomplete combustion reactions

Answer 11

• Occurs when the supply of oxygen is limited. Ex. in enclosed spaces
• Products: CO2, H20, CO, C, & some energy
• Flames are often sooty (soot=carbon particles), yellow, and cooler

Question 12

Carbon Monoxide poisoning

Answer 12

• Incomplete combustion reactions release carbon monoxide
• Excess amounts of carbon monoxide can result in headaches and difficulty in breathing
• Carbon monoxide binds to hemoglobin in our blood & does not allow the blood to carry oxygen as easily. Increased levels of carbon monoxide in the blood can result in death.
• SIGNS/SYMPTOMS: Headache, shortness of breath, chest pain, nausea/vomit, dizziness, collapse, loss of consciousness.

Question 13

Do combustion reactions occur fast or slowly?

Answer 13

Fast

Question 14

Types of Chemical Reactions: synthesis reactions

Answer 14

Occurs when 2 or more reactants combine to form one larger compound
- A significant amount of energy is released in the form of heat and/or light. (EXOTHERMIC REACTION)
- Synthesis reactions sometimes require a small amount of “start-up” energy to begin
Ex. Friction in striking a match against a rough surface provides activation/start-up energy.

RULE 1: element + element –> compound
RULE 2: compound + compound –> 1 compound
> Metal oxide + water –> metal hydroxide

Question 15

Types of Chemical Reactions: decomposition reactions

Answer 15

Occurs when a large compound breaks down into two or more compounds
- Opposite of synthesis reaction
- Most decomposition reactions require energy to break the bonds in the reactants (ENDOTHERMIC REACTION)

RULE 1:Binary compound –>element + element
RULE 2:Polyatomic compound –> compound + compound
> metal hydroxide –> metal oxide + water
> metal carbonate –> metal oxide + carbon dioxide
> metal chlorate –> metal chloride + oxygen

Question 16

Types of Chemical Reactions: single displacement reactions

Answer 16

Occurs when a free (single) metal can displace a metal in a compound if it’s more reactive.
- In order for the reaction to occur, the metal replacing must be more reactive (CHART ON YELLOW PAGE). If it’s less reactive the reaction won’t occur.
- The more reactive the metal the greater its activity is
- The bigger the gap between the 2 metals, the faster or more vigorous the reaction
- Treat hydrogen as a metal

Question 17

Free Halogens displacing halogen ions in compounds

Question 18

Types of Chemical Reactions: double displacement reactions

Answer 18

Occurs when 2 metals from different compounds displace each other
- Either a precipitate (solid), gas, or liquid must be formed as a product for it to be considered a double displacement reaction–> Note that (aq) is not considered a liquid

Question 19

A precipitate is

Answer 19

a solid formed when two aqueous solutions that are transparent (don’t have to be colourless but transparent) are mixed together.

Question 20

How come metals are willing to which partners in a double displacement reaction?

Answer 20

Bcuz the reactant compounds are in an aqueous solution, the ions are separated by water, and are kept apart. However, sometimes when you mix two aqueous solutions together, the water isn’t strong enough to keep the metal from the first solution from being attracted to the non-metal in the other one and the same thing happens with the other two. If the attraction is weak, water may be able to dissolve the new compounds into ions again and no reaction will occur. However if even one of the new compounds is strong enough, it will likely become a precipitate.

Question 21

Free Halogens displacing Halogen Ions in compounds

Answer 21

The free halogen that displaces the halogen ion in the compound must be more reactive (CHART ON BACK OF YELLOW SHEET)

Question 22

Double displacement reactions hat produce a gass

Answer 22

rmr acids typically start with or contain Hydrogen. Bases end in hydroxide

Metal carbonate reacts with acids to a produce 2 products, one of which will decompose into water (liquid) and CO2 (gas). CO2 bubbles will be observed

Metal sulfites reacts with acids to produce 2 products, one of which will decompose to produce water (liquid) and SO2 (solid). SO2 bubbles will be observed

Metal sulfides react with acid to produce 2 products, one of which be H2S (gas). H2S bubbles will be observed.

Ammonium salts react with bases to produce 2 products, one of which will decompose to produce water (liquid) and NH3 (gas). NH3 bubbles will be observed.

Question 23

Arrhenius Acids are

Answer 23

any species that increases the concentration of H+ ions - or protons- in aqueous solutions. –> Pretty much a compound that has H that can break into H+ ions when dissolved in water

Question 24

Arrhenius Bases are

Answer 24

any species that increases the concentration of OH- ions - or hydroxide- in aqueous solutions. –> Pretty much a compound that has OH that can break into OH- ions when dissolved in water

Question 25

Neutralization reactions

Answer 25

are a special case of double displacement reaction where water is formed.
- the end result is a mixture of neutral substances
Acid (PH<7) + Base (PH>7) –> H2O + salt (PH=7)

Question 26

Spectator ions are

Answer 26

ions that have not changed their state during a chemical reaction (im not sure if it just applies to double displacement)

Question 27

Total Ionic equation

Answer 27

shows all the ions in the reaction (SEE PAGE 23 IN CHAPTER 4 BOOKLET)

Question 28

Net Ionic equation

Answer 28

Show only the ions involved in the formation of the precipitate. (SEE PAGE 23 IN CHAPTER 4 BOOKLET)

Question 29

Selective Precipitation is

Answer 29

a technique of separating ions in an aqueous solution by using a reagent (reactant) that precipitates one or more of the ions, while leaving other ions in solution
- It’s an application of double displacement reactions
- the ions can then be separated through filtration or decanting
(SEE PAGE 26 IN CHAPTER 4 BOOKLET)