Chapter 7: Chemical Reactions and Quantities

What shows evidence of a chemical change?

• Formation of bubbles

• Change in color

• Production of a solid (precipitate)

• Heat produced or absorbed

How do you write a chemical equation?

reactant (state of matter) + reactant (state of matter) → product (state of matter) + product (state of matter)

What does the Law of Conservation of Mass state in relation to chemical formulas?

Chemical formulas follow the Law of Conservation of Mass

• No atoms are lost or gained

• Reactant side atoms = Product side atoms

  • g of reactants = g of products

What are the states of matter used in chemical formulas and what are their abbreviations?

Solid = (s)

Liquid = (l)

Gas = (g)

Aqueous = (aq)

What does aqueous mean?

A solution in which the solvent is water

• Dissolved in water

What does it mean when ∆ is above the arrow in a chemical formula?

The reactants are heated

• The reactions occur at a higher temperature

Diatomics

H₂, N₂, O₂, F₂, Cl₂, Br₂, I₂

• All still elements

• How these elements appear in nature (alone)

What can you change when balancing an equation? What can’t you change?

You can only change the coefficients

You cannot change the subscripts

What is the purpose of balancing equations?

To make sure there are the same amount of reactants as products

What does it mean when a compound starts with H?

It’s an acid

What does it mean when a compound has OH?

It’s a base

How would you display the number 1 when balancing an equation?

You would write nothing next to that element/compound.

Balance:

___H₂SO₄ + ___KOH → ____H₂O + ___K₂SO₄

___H₂SO₄ + ___KOH → ____H₂O + ___K₂SO₄

Reactants:

• H = 3

• SO₄ = 1

• K = 1

• O = 1

Products:

• H = 2

• SO₄ = 1

• K = 2

• O = 1

  Play around with the combinations until each of the vales matches up on both sides.

H₂SO₄ + 2KOH → 2H₂O + K₂SO₄

Reactants:

• H = 4

• SO₄ = 1

• K = 2

• O = 2

Products:

• H = 4

• SO₄ = 1

• K = 2

• O = 2

What are the types of chemical reactions? (list)

• Combination (synthesis)

• Decomposition

• Single Replacement (displacement)

• Double Replacement (displacement w/ ionic compounds)

• Combustion (burn)

What is a combination/synthesis reaction?

Two or more substances combine to form a single new substance

• Usually becomes larger

o + o → O

A + B → AB

What is a decomposition reaction?

When one reactant breaks down into two or more products

O → o + o

AB → A + B

How do you write an ionic compound? (order)

Metal first, then nonmetal

• Positive charge, negative charge

What is a single replacement reaction?

A reaction in which one element is substituted for another element in a compound

• If the lone element is a metal, it will kick out the other metal in the pair and vice versa with a nonmetal

A(metal) + BC → AC + B

A(nonmetal) + BC → BA + C

What are usually the reactant states of matter in a single replacement reaction?

The lone substance is a pure element, and the pair is an aqueous solution

What is a double replacement reaction?

Two compounds swap atoms forming two different compounds

• Switching partners

AB + CD → AD + CB

Which elements switch in a double replacement reaction?

The nonmetals

What happens with states of matter when it comes to double replacement reaction?

Of the two originally aqueous substances, one usually becomes a solid

• Very rarely both become a solid

What is a combustion reaction?

Many combustion reactions occur with a hydrocarbon and oxygen in order to make it burn.

• Uses the ∆ over →: to indicate heat

• Has the same products

CH (hydrocarbon) + O₂ → CO₂ + H₂O + energy

• Energy is usually not written in the formula, but it is always created

“Combustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel and an oxidant, usually atmospheric oxygen“

Which reactions will we be expected to determine the outcomes for?

Single and Double Replacement Reactions

When forming single and double replacement reactions, what must you always do after switching?

Make sure the compounds are all neutral (using what we learned in the last chapters)

• Balance the equations

Oxidation-Reduction Reactions

When electrons are transferred from one substance to another

• Talks about what happened to the reactants in a chemical reaction

What are specific uses of Oxidation-Reduction Reactions

Provide us with energy from food

• Provide electrical energy from batteries

Occurs when iron rusts

Oxidation

Loss of electrons

Reduction

Gain of electrons

What are free elements

Elements that are by themselves, not bound to any other elements = not a compound

Are diatomics free elements?

Yes

What are oxidation numbers and how do you write them?

The oxidation number of simple ions is equal to the charge on the ion = hypothetical charge

• In the same place as charges, but the pos/neg is switched

Charge = 2+

Oxidation Number = +2

How do you determine oxidation #’s?

Using the list of rules

• The higher up the rule is, the more accurate and likely it is correct

• Read and assign numbers from the top to the bottom of the list

Redox Reaction

Another name for an oxidation-reduction reaction

What type of reaction is always redox and which is always not.

Always Redox: Single Replacement

Never Redox: Double Replacement

Oxidation # Rules (1 - 5)

1. Free elements always have an oxidation state of 0

2. Monatomic ions have an oxidation state equal to their charge

   3a. The sum of all oxidation states of atoms in a compound is equal to 0 (ionic)

   3b. The sum of the oxidation states of all atoms in a polyatomic ion equals the charge on the ion

   4a. Group I metals have oxidation states of +1 in all their compounds

   4b. Group II metals have oxidation states of +2 in all their compounds

3. In their compounds, nonmetals have oxidation states according to the table/list ↓

• Nonmetals higher on the table/list take priority

F = -1

H = +1

O = -2

Grp 7A = -1

Grp 6A = -2

Grp 5A = -3

State the oxidation number for

• NO₃⁻

• NaCl

• H₂

NO₃⁻

The first rules don’t have much to do with this, except for #3 but we don’t have enough info to solve there. So instead we figure out that O is = to -2 from #5 now we can jump back up to #3

? + 3(-2) = -1 ? + -6 = -1 ? = +5 = N’s oxidation #

NaCl

From rule 2, we know they Na = +1 and Cl = -1 and we can confirm it works using rule 3

H₂

Using rule 1, we can determine that is free element has an oxidation state of 0

Avogadro’s Number

Contains 6.022 x 10²³ items

• Items = atoms, molecules, ions

• Used for magnitudes of sextillion

  • Molar quantity

What are small particles such as atoms, molecules, and ions counted using?

The mole

Mole → Particles Conversion

1 Mol = 6.022 x 10²³ particles

• Used like 1 dozen = 12 donuts

What is the conversion factor that can be set up using the mole and particles?

1 Mol/6.022 x 10²³ particles

OR

6.022 x 10²⁴ particles/1 Mol

Mole-Mole Ratios

The relationships within a formula

• The moles of each element in 1 mole of compound

• Based on subscripts = # of atoms

Mole-Mole Ratios

• For Aspirin = C₉H₈O₄

9 mol C/ 1 mole C₉H₈O₄

8 mol H/ 1 mole C₉H₈O₄

4 mol O/ 1 mole C₉H₈O₄

How many atoms of O in 0.150 moles of Aspirin (C₉H₈O₄)?

0.150 mol C₉H₈O₄ (4 mol O/1 mol C₉H₈O₄) = 0.600 mol O

0.600 mol O (6.02 x 10²³ atoms O/1 mol O) = 3.61 x 10²³ atoms of O

Molar Mass

• The mass of 1 mole of an element

• The atomic mass expressed in grams

How would you figure out the molar mass for

• O₂

• LiCO₃

O₂

First figure out the atomic mass, which is 16.00 for O, now we multiply by 2 for the # of atoms = 32.00g

LiCO₃

Figure out each atomic mass, multiply is necessary based on the # of atoms, in this case x 3 for the O

Then add all the values together = 66.95g

Consider significant figures as well

How can you use molar mass as a conversion factor?

Mole → grams or grams → moles

Ex. 1 mole O = 16.00 g

1 mol O/ 16.00 g O

OR

16.00 g O/ 1 mol O

Mole-Mole Factors from Equations

• 2Fe + 3S → Fe₂S₃

Fe and S = 2 mol Fe/3 mol S or flipped

Fe and Fe₂S₃ = 2 mol Fe/1 mol Fe₂S₃ or flipped

S and Fe₂S₃ = 3 mol S/1 mol Fe₂S₃ or flipped

Limiting Reactant

The substance that is used up first in a chemical reaction

• Limits the amount of product that can form

How do you determine the limiting factor?

Translating each reactant into product, so that you can compare “apples to apples“

2 bread + 1 cheese = 1 sandwich

***

3 cheese = 3 sandwiches

8 bread = 4 sandwiches

Cheese would be the limiting factor; it can make less of the product

How can you use limiting factor to determine the overall product made?

However much product the limiting factor creates, is the overall product creation

• The lesser value

Theoretical Yield

The max amount of product produced

• Determined using the equations

Actual Yield

The amount of product actually obtained

• In lab

What causes a difference in the theoretical and actual yield?

When the reaction does not go to completion, or some of the reactant or product is lost

Percent Yield

The ratio of actual yield to theoretical yield

Percent Yield Formula

actual yield/theoretical yield x 100%

What unit of measurement is yield calculated in?

Grams

What do you do with sigfigs when calculating percent yield?

Don’t round sig figs until AFTER using the percent yield formula

What does almost every chemical reaction involve?

The loss or gain of electrons

Enthalpy

Heat of Reaction

• Referred to as ∆H = Change in Enthalpy

What is enthalpy used for?

Determining whether a reaction was exothermic or endothermic

What are the SI Units for energy?

J = joules

kJ = Kilojoules; 1000 joules

Heat of Reaction

The amount of heat absorbed or released during a reaction that takes place at constant pressure

When does an energy change occur?

• Reactants interact

• Bond break apart

• Products are formed

What does ∆H represent?

The difference in energy of the products and the reactants

How do you calculate ∆H

∆H = ∆products - ∆reactants

What are the types of heat related reactions?

Exothermic and Endothermic

Exothermic Reaction

Heat is released

• The energy of the products is less than the energy of the reactants

• Heat is a product

• ∆H is negative

H₂(g) + Cl₂(g) → 2HCI(g) + 185 kJ

∆H = -185 kJ

Endothermic Reaction

Heat is absorbed

• The energy of the products is greater than the energy of the reactants

• Heat is a reactant (added)

• ∆H is positive

N₂(g) + O₂(g) + 180 kJ → 2NO(g)

∆H = +180 kJ

Energy Diagrams

Used to display exothermic and exothermic reactions

What would an exothermic energy diagram look like?

Reactants higher than products, curve goes down

• Energy release →↑

What would an endothermic energy diagram look like?

Products higher than reactants, curve goes up

• Energy absorbing →↑

What does → and ↑ mean in an energy diagram?

↑ = energy increase

→ = reaction progress

Stoichiometry

The relationship between the relative quantities of substances taking part in a reaction or forming a compounds

What is the difference between charges and oxidation states?

The formal charge determines the number of electrons that occur around an atom of a molecule while oxidation state determines the number of electrons exchanged between atoms during the formation of a molecule.