# a – An effective collision of reactant molecules produces product molecules. b

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a – An effective collision of reactant molecules produces product molecules.

b – An ineffective collision of reactant molecules produces no reaction, and the reactants bounce apart unchanged.

Rate of Reaction (Reaction Rate) – how fast a reaction takes place
 Reaction Rate Speed (Faster or Slower?) Duration (More or less time?) Increases FASTER LESS Time Decreases SLOWER MORE Time

Rate of Reaction (Reaction Rate): how fast a reaction takes place

• When the rate of reaction increases, the time that it takes for a reaction to take place ___decreases___.

(decreases/increases)

• When the rate of reaction decreases, the time that it takes for a reaction to take place ___increases___.

(decreases/increases)
Factors Affecting Reaction Rate NOTES
1. Concentration – a measure of the amount of solute that is dissolved in a given quantity of solvent.

• As concentration increases, the number of reacting particles present __ increases _

(decreases/increases)

and therefore the frequency of collisions _ increases _.

(decreases/increases)

• Reaction rate increases (reaction is faster ) with a(n) _ increase_ in concentration. (faster/slower) (decrease/increase)

Ex. Aluminum dissolves faster in…….? 2M HCl or 10M HCl

2. Temperature – a measure of the average kinetic energy (KE) of particles.

• As temperature increases, molecules have greater KE (moving faster) and therefore _ more collisions occur. (more/less)

• Reaction rate increases with a(n) _ increase _ in temperature.

(decrease/increase)

Ex. Sugar dissolves faster in…….? H2O(l) @ 30°C or H2O(l) @ 90°C

3. Surface area – a measure of how much exposed area an object has.

• As surface area increases the particles have a greater area for collisions to occur and therefore _ more_ effective collisions take place.

(more/less)

• The smaller the particle size, the greater the surface area.

(greater/smaller)

• Reaction rate increases with a(n) _ increase __ in surface area.

(decrease/increase)
Ex. Which will dissolve faster in hot coffee? Cube of sugar or Crushed sugar
IT IS ONLY POSSIBLE TO ALTER THE SURFACE AREA OF A SUBSTANCE IN THE SOLID PHASE!

4. Addition of a Catalyst – A catalyst is a substance that speeds up the reaction by providing “an alternate path” for the reaction to occur. A catalyst requires a lower activation energy (energy needed for the reaction to occur).

Reaction Rate Factors Check (NOTES):

Be sure you “get” reaction rates and the factors that affect them by matching the numbered phrases on the right to the boxes on the left so that the order of cause and effect is correct.

A reaction is cooled

1 – the reaction to proceed slower

2 – particles to move slower

3 – the reaction rate to decrease

4 – less particle collisions to take place

– electron releases energy

causes

2

c

4

auses
causes

1

63

3

3

and

A reactant is made more concentrated

1 – more particle collisions to take place

2 – more particles to be present

3 – the reaction rate to increase

4 – the reaction to proceed in less time

– electron releases energy

causes

2

c

1

auses
causes

4

6

33

and

Reaction Rate Factors Check cont’d

A large chunk of reactant is used

1 – the reaction to proceed slower

2 – the reaction rate to decrease

3 – fewer particle collisions to take place

4 – less exposed surface for collisions (lower surface area)

– electron releases energy

causes

6

4

c

3

auses
causes

1

6

232

and

Assigning Oxidation Number NOTES:
1.) The overall charge on an atom is: neutral (zero)
2.) The overall charge on an ion is: positive or negative
3.) Charges are also called oxidation states (numbers). This name comes from the process known as oxidation, which occurs when atoms lose electrons to become positively charged ions.
4.) What charge does bromine have? 0
5.) What charge does bromine have when it is bonded to potassium? -1
6.) How are both a bromine atom and a bromide ion shown on the periodic table? For an atom, the atomic

number & total number of electrons in the electron configuration are the same. For the ion, the possible

charges are listed in the upper right hand corner.

7.) Assign oxidation numbers for the ionic compound: Ca+2Cl2-1

FOLLOW THE RULES ON THE PREVIOUS PAGE FOR ASSIGNING OXIDATION NUMBERS!
9.) Try these compounds containing transition metals and/or polyatomic ions:

Fe2+3O3-2 Fe+2(S+6O4-2) Fe+3(N+5O3-2)3-1

10.) Covalent compounds do NOT form ions with charges but we will learn that each element in a covalent compound has a different ability to pull the electrons toward it, resulting in different areas of charge (called poles, not ions) within a covalent compound. We will learn about this in Unit 8… for now, just assign oxidation numbers to covalent compounds the same way that you do to ionic ones.
Practice: C+4O2-2

NOTES: REDOX REACTIONS
YOU MUST USE THE FOLLOWING PROCESS TO DETERMINE IF YOU HAVE

A REDOX REACTION!
We will use the following balanced chemical equation to help you through the process:
2 Na + Cl2 2 NaCl
Step 1: Assign all oxidation numbers (this is always the first step, even if the problem doesn’t tell you to!)
It is best to write the oxidation numbers above the equation
Example: 2 Na0 + Cl20  2 Na+1Cl−1
Step 2: Decide if we have a type of chemical reaction called Oxidation-Reduction also known as Red-ox Reactions.
You can tell if you have a redox reaction by looking at the oxidation numbers for each atom in the reactants and each atom of the same type in the products. If there was a change in the oxidation number for a particular type of atom, then it must be a redox reaction.
**PLEASE NOTE: If one atom had an increase in oxidation state, there must be a different type of atom with a decrease in oxidation state. If this is not true, you assigned you oxidation numbers wrong. Check your work!
Example: Na’s charge changed from 0 to +1

Cl’s charge changed from 0 to −1
Step 3: If you have determined you have a redox reaction, you need to pick out what is being oxidized and what is being reduced. A species, in the chemical sense, is the part of the compound being oxidized or reduced.

LOSING ELECTRONS RESULTS IN AN

• INCREASE IN POSITIVE CHARGE (or a decrease in negative charge)

• INCREASE IN OXIDATION NUMBER AND IS CALLED OXIDATION

GAINING ELECTRONS RESULTS IN AN

• INCREASE IN NEGATIVE CHARGE (or a decrease in positive charge)

• DECREASE IN OXIDATION NUMBER AND IS CALLED REDUCTION

Therefore, the reacting species whose oxidation state decreased (went down) was reduced. The reacting species that had its oxidation number go up in value was oxidized.

If you take a minute to think about this, it should make sense… Reduction is the gain of electrons and electrons are negative, so it makes sense if you are gaining negatives your oxidation number would go down, hence reduction. Oxidation is loss of negatives so your number goes up.
Example: Na was oxidized, Cl2 was reduced

LEO↑ says GER↓
LEO = Loss of Electrons is Oxidation / GER = Gain of Electrons is Reduction

Optional Mini-Lesson: Oxidation & Reduction
1. Label each of the arrows below as oxidized or reduced.
oxidized

-4 -3 -2 -1 0 1 2 3 4

reduced

2. Oxidation states are assigned to denote charges that atoms acquire (get) when they lose or gain electrons. Chemists show this in an equation such as:

_2_Al0+ _3_Cu+2Cl2-1 → _2_Al+3Cl3-1 + _3_Cu0
a. Balance the equation.
The first step in determining which species (just another way to say which element) lost electrons during this reaction is to ASSIGN OXIDATION NUMBERS. Do this now!
b. Which species gained electrons during this reaction? Cu+2

Which species lost electrons during this reaction? Al0

c. Can any reaction occur in which electrons are lost but not gained, or gained but not lost? Why?
No! If electrons are lost, they MUST be gained by something else. Likewise, if electrons are gained they HAVE to be lost by something else. Otherwise the conservation of charge will be violated. The number of electrons lost must equal the number of electrons gained.
To show conservation of charge, the same number of electrons must be lost and gained!!

Optional Review Mini-Lesson From Unit 3:

“Determine the chemical formula of a compound, given its IUPAC name.”

To turn a chemical name into a chemical formula, ask yourself the following:

1. Is there a roman numeral in the name?

1. If no, it is not a transition metal, so look at the reference table for the electron configuration and determine what charge the metal and nonmetal ions would have.

2. If yes, the roman numeral is the charge associated with the transition metal. Turn the roman numeral into a charge, and look up the charge of the nonmetal from the reference table.

2. Use these charges to determine the ratio of ions that are needed, and therefore the subscripts of the compound.

Write formulas for the following:

 potassium iodide KI nickel (III) oxide Ni2O3 barium chloride BaCl2 manganese (IV) sulfate Mn(SO4)2 sodium phosphide Na3P barium carbonate BaCO3 tin (IV) oxide SnO2 aluminum hydroxide Al(OH)3 gold (III) bromide AuBr3 potassium permanganate KMnO4 copper (II) iodide CuI2 lithium sulfate Li2(SO4) silver oxide Ag2O ammonium nitride (NH4)3N chromium (III) sulfide Cr2S3 calcium hydroxide Ca(OH)2 iron (II) sulfite Fe(SO3) beryllium nitride Be3N3 magnesium chloride MgCl2 chromium (IV) bromide CrBr4

REHAB-Assignment #A: Redox Reaction Skill Drills

Skill #1 – Assigning Oxidation Numbers (Text Reference: p. 639 – 641)

All elements have an oxidation number of 0. In compounds, oxidation numbers add up to 0.

• Group 1 elements are +1 in all compounds.

• Group 2 elements are +2 in all compounds.

• F is always -1 in compounds.

• H is usually +1, and if so, will be first written in the chemical formula.

• O is almost always -2, exceptions: H2O2 and OF2

• In compounds using polyatomic ions, the first and middle elements all have + oxidation states.

Sulfur has 5 oxidation states: -2, 0, +2, +4, +6

1. Which substance listed below has sulfur with an oxidation state of “0”? How do you know?

1. H2S 2. S 3. SO3 4. SO2

S isn’t in a compound – it’s a free element!

1. In the compound Na+12S+22O−23, does S have a + or – oxidation state? +

What is the oxidation number of S in each of the following substances?

1. H2S -2 5.) SO2 +4 7.) SO3 +6

1. S 0 6.) Na2S2O3 +2

Chlorine has six possible oxidation states that it uses in bonding situations: -1, 0, +1, +3, +5, +7

What is the oxidation number of Cl in each of the following substances?

8.) HClO4 +7 10.) HClO2 +3 12.) NaCl -1
9.) HClO3 +5 11.) HClO +1 13.) Cl2 0
Hydrogen has three oxidation states: -1, 0, +1

What is the oxidation number of H in each of the following substances?

14.) LiH -1 15.) H2O ____+1____ 16.) H2S ___+1_____ 17.) H2 ____0____
Oxygen is usually -2 in compounds, but may be -1 or +2 in weird situations

What is the oxidation number of O in each of the following substances?

18.) H2O -2 21.) NaOH -2
19.) O2 0 22.) H2SO3 -2
20.) OF2 +2 23.) Na2O2 -1
Nitrogen has an amazing nine oxidation states! -3, -2, -1, 0, +1, +2, +3, +4, +5

Assign an oxidation state to N in each compound:

24.) NO2 +4 25.) HNO3 +5 26.) Li3N __-3_____ 27.) NH3 ____-3____

REHAB-Assignment #B: Redox Reaction Skill Drills (cont’d)

Skill #2 – Identifying Redox Reactions (Text Reference: p. 645 – 647)

In all reactions, both mass and charge must be “conserved” (maintained).

If an equation involves a free element (an element by itself), it is a redox reaction.

Double replacement reactions are NEVER redox, but the other 4 types USUALLY are.

1.) Which equation is an example of an oxidation-reduction reaction? Two answers! (oops!)

1. C3H8 + 5 O2 3 CO2 + 4 H2O 3. Cu + 2AgNO3 Cu(NO3)2 + 2Ag

2. HCl + NaOH  HOH + NaCl 4. Pb(NO3)2 + 2NaI  2NaNO3 + PbI2

2.) In a redox reaction, there is conservation of

1. mass, only 2. charge, only 3. both mass and charge 4. neither mass nor charge

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