Test 3: Stoichiometry

Question 1

What is stoichiometry, what does it discuss

Answer 1

Discusses relationship between the amounts of the reactants used and the amounts of products produced

Question 2

What are the six types of elemental reactions

Answer 2

Synthesis
Decomposition
Single Replacement
Neutralization
Double Replacement
Combustion

Question 3

How is reforming bonds with different atoms more stable

Answer 3

More stable by having less energy than before (Release energy)

Question 4

Whats another name for single replacement reactions, what is formed in a doublle replacemet reaction

Answer 4

Forms a precipitate (solid)
Redox reaction

Question 5

What do acids and bases tend to do in neutralization reactions (think giving away, accepting)

Answer 5

Acids give away H+ (Getting rid of protons)
Bases accept H+

Question 6

What are the reactants and products of a combustion and neutralization reaction

Answer 6

Neutralization: acid + base = water + salt
Combustion: hydrocarbon + oxygen = carbon dioxide + water

Question 7

What does enthalpy mean

Answer 7

The amount of energy stored in the bonds of the reacctants or products in a system

Question 8

What do changes in enthalpy result from

Answer 8

Results from energy that is given off to the surroundings or absorbed as heat

Question 9

What is the formula for change in enthalpy

Answer 9

Change in enthalpy= enthalpy of products (Hproducts) - enthalpy of reactants (Hreactants)

Question 10

Where does potential energy of a molecule come from

Answer 10

The energy in a chemical bond form most of the potential energy

Question 11

When forming a bond, is energy released or absorbed?

Answer 11

Released (bond is lowest energy state, so “excess” energy is gone)

Question 12

When breaking a bond, is energy released or absorbed?

Answer 12

Absorbed (takes energy to overcome intramolecular forces of molecules)

Question 13

When do endothermic reactions occur

Answer 13

If more energy is absorbed (bonds breaking) than is released (bonds forming)
Net absorption of energy

Question 14

When do exothermic reactions occur

Answer 14

If more energy is released (bonds forming) than energy required to break the intial bonds
Net release of energy

Question 15

Whats the activation complex

Answer 15

When all bonds start to break and reform

Question 16

Whatre some properties of endothermic reactions, whats the change in enthalpy

Answer 16

Change in enthalpy is positive (more energy in products)
Feels colder
Absorbes energy from surroundings (you)

Question 17

How is energy stored in endothermic reactions, whats the thermochemical equation

Answer 17

Stored not as heat, but conservation energy
H+A=B (sorry no arrows)

Question 18

Whatre properties of exothermic reactions, whats the change in enthalpy, whats the thermochemical equation

Answer 18

Change in enthalpy is negative (products have less energy)
Feels hotter
Releases energy into surroundings
A= B+ H (sorry theres no arrow)

Question 19

Which reaction do systems favour more

Answer 19

Lower energy states (exothermic, lowest enthalpy)

Question 20

Whats a limiting reagent

Answer 20

Reactant that runs out first (true theoretical yield)

Question 21

Whats an excess reagent

Answer 21

Reactant that has left over

Question 22

How do you find which reactant is the excess and which is the limiting

Answer 22

Calculate how much product is made from both given values of each reactant, the one that makes less product is the limiting

Question 23

Whats theoretical yield

Answer 23

The amount of product expected (calculated using stoichiometry)

Question 24

Whats actual yield

Answer 24

The actual amount of product made from an experiment

Question 25

How do you calculate percent yield? What does it mean

Answer 25

Means how accurate the experiment is
(Actual yield divided by theoretical yield) multiplied by 100

Question 26

How do you calculate the percent purity

Answer 26

(Mass of pure substance divided by mass of impure substance) multiplied by 100