Test 3: Stoichiometry Flashcards
What is stoichiometry, what does it discuss
Discusses relationship between the amounts of the reactants used and the amounts of products produced
What are the six types of elemental reactions
Synthesis
Decomposition
Single Replacement
Neutralization
Double Replacement
Combustion
How is reforming bonds with different atoms more stable
More stable by having less energy than before (Release energy)
Whats another name for single replacement reactions, what is formed in a doublle replacemet reaction
Forms a precipitate (solid)
Redox reaction
What do acids and bases tend to do in neutralization reactions (think giving away, accepting)
Acids give away H+ (Getting rid of protons)
Bases accept H+
What are the reactants and products of a combustion and neutralization reaction
Neutralization: acid + base = water + salt
Combustion: hydrocarbon + oxygen = carbon dioxide + water
What does enthalpy mean
The amount of energy stored in the bonds of the reacctants or products in a system
What do changes in enthalpy result from
Results from energy that is given off to the surroundings or absorbed as heat
What is the formula for change in enthalpy
Change in enthalpy= enthalpy of products (Hproducts) - enthalpy of reactants (Hreactants)
Where does potential energy of a molecule come from
The energy in a chemical bond form most of the potential energy
When forming a bond, is energy released or absorbed?
Released (bond is lowest energy state, so “excess” energy is gone)
When breaking a bond, is energy released or absorbed?
Absorbed (takes energy to overcome intramolecular forces of molecules)
When do endothermic reactions occur
If more energy is absorbed (bonds breaking) than is released (bonds forming)
Net absorption of energy
When do exothermic reactions occur
If more energy is released (bonds forming) than energy required to break the intial bonds
Net release of energy
Whats the activation complex
When all bonds start to break and reform
Whatre some properties of endothermic reactions, whats the change in enthalpy
Change in enthalpy is positive (more energy in products)
Feels colder
Absorbes energy from surroundings (you)
How is energy stored in endothermic reactions, whats the thermochemical equation
Stored not as heat, but conservation energy
H+A=B (sorry no arrows)
Whatre properties of exothermic reactions, whats the change in enthalpy, whats the thermochemical equation
Change in enthalpy is negative (products have less energy)
Feels hotter
Releases energy into surroundings
A= B+ H (sorry theres no arrow)
Which reaction do systems favour more
Lower energy states (exothermic, lowest enthalpy)
Whats a limiting reagent
Reactant that runs out first (true theoretical yield)
Whats an excess reagent
Reactant that has left over
How do you find which reactant is the excess and which is the limiting
Calculate how much product is made from both given values of each reactant, the one that makes less product is the limiting
Whats theoretical yield
The amount of product expected (calculated using stoichiometry)
Whats actual yield
The actual amount of product made from an experiment
How do you calculate percent yield? What does it mean
Means how accurate the experiment is
(Actual yield divided by theoretical yield) multiplied by 100
How do you calculate the percent purity
(Mass of pure substance divided by mass of impure substance) multiplied by 100
