4.1-4.2 Flashcards
Assumption 1
Reactions are processes in which atoms that make up the reactants are rearranged, producing new substances.
Conservation of all atoms = mass & number of atoms
Assumption 2
Rearranging atoms involves redistribution of electrons, changing potential energy of the particles. This explains why all chemical reactions involved the transfer of energy to the surroundings.
Endothermic reactions
Reaction in which a large amount of energy must be input for the reaction to go forward
Reactants A have low PE and few configurations, Products B have high PE but more configurations.
Exothermic reactions
Reaction in which little energy is required.
Reactants C high PE low configurations, Products D low PE high configurations.
Assumption 3
For a reaction to occur, particles must collide. More collisions makes a faster process
Higher temp, higher pressure, higher concentration
Assumption 4
Colliding particles must be oriented in a manner that allows reacting groups to interact effectively.
Limiting reactant
A reactant of where there is too little according to the balanced chemical equation, causing an excess of another reactant
Higher potential energy of a substance =
weaker bonds
Configuration effectiveness
higher % of configurations leading to effective collision, faster process
In general,
1. fewer number of particles in gas phase that need to interact to generate particles
2. simpler the composition and structure of particles in the reactants
The faster the reaction goes
Assumption 5
For a reaction to occur, particles must have enough energy to reach a transition state that leads to the formation of new products - activation energy
Catalysts - lower activation energy
Assumption 6
As reactants interact to generate products, particles of the products may chemically react and regenerate particles of the reactants. The final state is determined by the balance between these two opposite processes.
Reactant favored
There are more particles of the reactants than the products
Product favored
There are more particles of the reactants than the products
Reaction extent
Determined by activation energy, collision effectiveness of forward and backward reaction
Conversion of reactants to products is close to 100% when…
the probability of forward reaction is much greater than the probability of the backward process during a cheical reaction
Theoretical yield
The theoretical maximum amount of product in a chemical reaction assuming it goes to completion
Case 1 (amounts of products)
There is only 1 reactant or all reactants are in excess except 1.
In all experimental situations, there are losses in the amounts of product formed tue to a variety of reasons
- Experiment (actual) yield will be different from theoretical yield.
actual/theoretical x 100 = % yield
- If yield is 100%, we will produce less product or need more of a reactant to produce the desired amount of product.
Case 2 (amounts of products)
If we are uncertain about which reactants are in excess and which is the limiting, we need to take systemic steps to identify it.
Chelation
Chelating agents are capable of grasping metal ions - EDTA has six sites you can use
Titration
Slowly adding a solution to a second solution until a stoichiometric equivalence is established
Indicator
substance that undergoes a color change with a slight molar excess - point where it is observed is the end point - Eriochrome Black T
Formation of EDTA
Ca2+ and EDTA4- = [Ca.(EDTA)]2-
mL of EDTA to ppm of CaCo3
mL EDTA = 1L/1000mL = .005 M/L = 3.95 x 10^-5 mol CaCo3 = (3.95 x 10^5 mol CaCo3)/volume x 10^6
Nitric acid
HNO3 = H+ and NO3-
strong acid, 100% dissociation
Nitrous acid
HNO2 = H+ and NO2-
weak acid, HNO2 is mainly undissociated
