Core inorganic and physical chemistry for forensic science Flashcards
What does the state in which a substance exist depend upon?
The competition or balance between intermolecular forces and thermal energy
What is the equation for pressure?
Force/area
What is mechanical equilibrium?
Equality of pressure
Define diathermic
Thermally conducting
Define adiabatic
Thermally insulating
Define thermal equilibrium
No change of state occurs when two object are in contact through a diathermic boundary
Zeroth Law of Thermodynamics
If A is in thermal equilibrium with B, and A is in thermal equilibrium with C, then C is also in thermal equilibrium with B
Charles’ Law
At a constant pressure, the volume of a fixed mass of gas is proportional to its pressure
Boyle’s Law
Provided temperature is kept constant, the volume of a fixed mass of gas is inversely proportional to its pressure
Law of combining volumes (Gay-Lussac)
At any given p and T, the volumes of gases that react with one another are in the ratios of small whole numbers
Avogadro’s hypothesis
equal volumes of gases at the same p and T contain an equal number of molecules
Avogadro’s Law
volume of a gas maintained at a constant pressure and temperature is directly proportional to the number of moles in the gas
what assumptions were made about the ideal gas law
there are no intermolecular forces in the gas, and gas molecules have no volume
what is the critical point
a set of conditions under which a liquid and its vapour become identical
system
part of the world in which we have special interest
surroundings
region outside the system where we make our measurements
what is work defined as
motion over some distance against an opposing force
what is the equation for work when pressure is constant
-P x change in V
Name the 3 ways the energy of a system may be changed other than work itself
heat (energy change results from a temperature difference between system and surroundings), exothermic process, endothermic process
what is the difference between endothermic and exothermic
exothermic is when energy is transferred as heat to the surroundings, endothermic is when energy is acquired from its environment as heat
define internal energy (U)
total energy of a system
define the first law of thermodynamics
the change in energy of a system is equal to the sum of the work done on the system and heat put into the system
what is the equation for the change in U
q + w
define calorimerty
study of heat transfer during physical and chemical processes
define calorimeter
device for measuring energy transferred as heat
define adiabatic process
transfer of energy in the form of work only
define thermochemistry
the study of energy transferred as heat during the course of chemical reactions
what is the enthalpy change for an exothermic reaction
< 0, negative
define standard enthalpy change
the change in enthalpy for a process in which the initial and final substances are in their standard states
define standard enthalpy of transition
the standard enthalpy change that accompanies a change of physical state
define the standard enthalpy of sublimation
a change in enthalpy independent of the path between two states
define Hess’s law
the overall enthalpy change of a reaction is independent regardless of the route taken
define standard enthalpy of formation
the enthalpy change to form a compound from its elements under standard conditions with all products and reactants in their standard states
define mean bond enthalpy
the average enthalpy change associated with the breaking of a specific bond
define Kirchoff’s Law
standard reaction enthalpies at different temperatures can be calculated from the heat capacities at constant pressure
define spontaneous reactions
those that, once started, will continue without any outside intervention
define the second law of thermodynamics
the state of entropy of the entire universe, as an isolated system, will always increase over time
Define the third law of thermodynamics
the entropy of a pure crystalline substance at absolute zero is zero
If G<0…
the reaction is spontaneous in the forward direction
If G=0…
the reaction is at equilibrium
If G>0…
the reaction is non-spontaneous in the forward direction but the reverse direction is spontaneous
name the 4 factors which affect reaction states
physical state of reactions, reactant concentrations, reaction temperature, the presence of a catalyst
define chemical rate
the change in the concentration of reactants or products per unit of time
define reaction rate
either the rate of the disappearance of A or the rate of the appearance of B
equation for rate
concentration/time
what are the four ‘rules’ for collision theory
particles must collide before reaction, not all collisions lead to reactions, reactions must have an activation energy, for the reaction to occur the molecules must collide at a specific orientation
define steric hinderance
when molecules are large so it is harder for them to collide at the correct orientation
what are the 4 factors rate of reaction can be increased by
increasing surface area, increasing concentration, increasing temperature, using a catalyst
define first order
when the rate doubles, the concentration doubles
define second order
when the concentration doubles, the rate quadruples. It is the square of what happens to the concentration
define half-life
the time required for the concentration of a reactant to react half of its initial value
define heterolysis
one of the atoms gains both electrons and becomes negatively charged
define homolysis
each atom keeps one of the bonding pairs of electrons, forming free radicals
define rate determining step
slowest step which limits the overall reaction rate
define the effective nuclear charge (Zeff)
the amount of positive charge experienced by an electron from the nucleus
what is the equation for Zeff
Z-S, where Z is the nuclear charge and S is the shielding constant
describe the trends of effective nuclear charge
increases across a period as protons are added to the nucleus, and increases down a group as the increase in protons is offset by the increased number of shielding electrons
describe the trends in orbital energies
increase down a group as they increase with the value of n, and decrease across a period because n remains unchanged and Zeff dominates
describe the trends in atomic size
decreases across a period due to increasing Zeff, and increases down a group as orbitals with a higher n have larger radii
define ionisation energy
the energy required to remove one electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions
describe the trends in ionisation energy
increases across a period due to increasing Zeff, and decreases down a group as there is lower nuclear attraction
define electron affinity
the energy required to add an electron to each atom in one mole of gaseous atoms to form one mole of 1- ions
describe the trends in electronegativity
decreases down a group as atomic radius and shielding are increasing, and increases across a period due to an increase in nuclear charge and a decrease in atomic radius
define electronegativity
measure of the tendency of an atom to attract a bonding pair of electrons
define redox reaction
process of electrons being transferred between species, both oxidation and reduction occur
define reducing agent
species which donates electrons, the species itself is oxidised
