Chemistry 2 Flashcards
compounds
pure substances composed of two or more elements in a fixed proportion
molecule
- combination of two or more atoms held together by covalent bonds.
- smallest unit of a compound that displays the identifying properties of that compound.
molecular weight
sum of the atomic weights of all the atoms in a molecule, and its units are atomic mass units (amu).
formula weight
adding up the atomic weights of the constituent ions according to its empirical formula
gram equivalent weight
where n is the number of protons, hydroxide ions, electrons, or monovalent ions “ produced” or “ consumed” per molecule of the compound in the reaction.
For example, you would need 49 grams of H2SO4 (molar mass = 98 g/mol) to produce one equivalent of hydrogen ions, because each molecule of H2SO4 can donate two hydrogen ions (n = 2).
Equivalents
Normality
- measure of concentration.
- units for normality are equivalents/liter
- where n is the number of protons, hydroxide ions, electrons, or monovalent ions “ produced” or “ consumed” per molecule of the compound in the reaction.
What is the molarity of a 1 N acid solution consisting of dissolved HCl?
….of H2SO4?
In a 1 N acid solution consisting of dissolved HCl, the molarity of HCl is 1 M because HCl is a monoprotic acid,
but if the dissolved acid is H2SO4, then the molarity of H2SO4 in a 1 N acid solution is 0.5 M, because H2SO4 is a diprotic acid.
Will one mole of HCl will not completely neutralize one mole of Ca(OH)2?
NO
one mole of HCl will not completely neutralize one mole of Ca(OH)2, because one mole of HCl will donate one equivalent of acid but Ca(OH)2 will donate two equivalents of base
law of constant composition
any pure sample of a given compound will contain the same elements in an identical mass ratio
percent composition by mass
combination reaction
two or more reactants forming one product
Ex:
decomposition reaction
A single compound reactant breaks down into two or more products, usually as a result of heating or electrolysis.
single-displacement reaction
an atom (or ion) of one compound is replaced by an atom of another element
(Single-displacement reactions are often further classified as redox reactions)
double-displacement reactions
(metathesis)
- elements from two different compounds swap places with each other (hence, the name double-displacement) to form two new compounds
- occurs when one of the products is removed from the solution as a precipitate or gas or when two of the original species combine to form a weak electrolyte that remains undissociated in solution
Neutralization reactions
specific type of double-displacement reaction in which an acid reacts with a base to produce a salt
Net ionic equations
Net ionic equations list only the elements important for demonstrating the actual reaction that occurs during a displacement reaction
vs.
For problems involving the determination of the limiting reactant, you must keep in mind two principles
- All comparisons of reactants must be done in units of moles. Gram-to-gram comparisons will be useless and maybe even misleading.
- It is not the absolute mole quantities of the reactants that determine which reactant is the limiting reactant. Rather, the rate at which the reactants are consumed (the stoichiometric ratios of the reactants) combined with the absolute mole quantities determines which reactant is the limiting reactant.
Percent yield
Calculate % Yield
Balanced equations (order)
Balanced equations are determined using the following steps in order:
- Balancing the non-hydrogen and non-oxygen atoms
- Balancing the oxygen atoms, if present
- Balancing the hydrogen atoms, if present
- Balancing charge when necessary
mechanism
series of steps by which a reaction proceeds
What is the rate expression
For the general reaction aA + bB → cC + dD
?
Rate is expressed in the units of moles per liter per second (mol/L· s) or molarity per second (M/s).
rate law
where k is the reaction rate coefficient or rate constant. Rate is always measured in units of concentration over time; that is, molarity/second. The exponents x and y (or x, y, and z, if there are three reactants, etc.) are called the orders of the reaction: x is the order with respect to reactant A, and y is order with respect to reactant B.
overall order of the reaction
sum of x + y (+ z… )
Qc < Keq, Δ G < 0
reaction proceeds in forward direction
Qc = Keq, Δ G = 0,
reaction is in dynamic equilibrium
Qc > Keq, Δ G > 0
reaction proceeds in reverse direction
The Law of Mass Action
The Reaction Quotient
For example, consider the formation of HCl from H2 and Cl2. The overall reaction is
What does the energy diagram look like?
Figure 5.2 shows that the reaction is exothermic. The potential energy of the products is less than the potential energy of the reactants; heat is evolved, and the enthalpy change of the reaction is negative.
What is ΔH for an exothermic reaction?
– Δ H = exothermic = heat given off
What is Δ H for an endothermic reaction?
+Δ H = endothermic = heat absorbed
How does a catalyst effect the energy of a reaction?
Consider the reaction:
It will shift to the RIGHT if…
- A or B added
- C removed
- pressure increased or volume reduced
- temperature reduced
Consider the reaction:
It will shift to the LEFT if…
- C added
- A or B removed
- volume increased or pressure reduced
- temperature increased
What is an “isolated system”?
The system cannot exchange energy (heat and work) or matter with the surroundings; for example, an insulated bomb calorimeter.
What is a “closed system”?
The system can exchange energy (heat and work) but not matter with the surroundings; for example, a steam radiator.
What is an “Open System”?
The system can exchange both energy (heat and work) and matter with the surroundings; for example, a pot of boiling water.
Adiabatic processes
occur when no heat is exchanged between the system and the environment; thus, the heat content of the system is constant throughout the process.
isobaric processes
occur when the pressure of the system is constant. Isothermal and isobaric processes are common, because it is usually easy to control temperature and pressure.
isothermal processes
occur when the system’s temperature is constant.
standard temperature and pressure (STP)
temperature is 0° C (273 K) and pressure is 1 atm.
standard conditions
The standard conditions are defined as 25° C (298 K) and 1 atm.