CHEM14BE

thermodynamics

study of energy and its interconversions

spontaneous process

does not require energy input

first law of thermodynamics

internal energy of a system is constant

second law

entropy of a system increases in the course of any spontaneous change

third law

the entropies of all perfect crystals approach zero as the absolute temperature approaches zero

kinetic energy

energy associated with the motion of an object

potential energy

energy associated with the position or composition of an object

energy

the capacity to do work and the capacity to transfer heat

work (w)

force acting over a distance

heat (q)

the transfer of energy caused by temperature difference

law of conservation of energy

energy cannot be created nor destroyed it can be converted or transferred

system

part of the universe of immediate interest in a particular experiment or study

surroundings

the remainder of the universe that lies outside the systems boundaries (everything the system can exchange energy with)

open system

matter and energy can be exchanged

closed system

matter can’t be exchange, energy can

isolated system

neither matter nor energy can be exchanged

thermodynamic property

a measurable property of thermodynamic systems

determined by the behavior of atoms/molecules in the system

thermodynamic state

condition of a system at a specific time

determine by the value of all of the thermodynamic properties of the system

calculating change in any thermodynamic property

change in X = Xfinal-Xinitial

path function

quantity in thermodynamics

value depends on the path between two thermodynamic states

state function

value depends only on the state of the system, not on how the system got to that state

kinetic molecular theory

models gases as a collection of particles in constant motion

formula for pressure

pressure = force/area of the surface

ideal gases

low pressure, high temperature

what is volume inversely proportional to?

pressure

internal energy

the total energy of a thermodynamic system

Ek

kinetic energy of all particles in a system due to their motion

Ep

potential energy of all particles in a system due to their interactions with one another

delta U=

q (heat) + w (work)

work =

-Pex x delta V

reversible processes

a process that occurs by making an infinitesimally small change to a thermodynamic property of the system

do not occur in real life

irriverisble process

a change in the system prevents the system from returning to equilitbrium

irreversible expansion work equation

w = -Pex x delta V

reversible expansion work equation

w=-nrtlnVf/Vi

thermal motion

disorderly motion of particles in a system

thermal energy

energy of the system due to thermal motion

temperature (t)

measure of the thermal energy within a sample of matter

proportional to energy

heat (q)

path function that describes the transfer of thermal energy between a system and the surroundings resulting from a temperature difference

specific heat capacity

the amount of heat required to raise temperature of 1 gram of a substance by 1 degree celsius

molar heat capacity

the amount of heat required to raise the temperature 1 mole of a substance by 1 degree celsius

spontaneous process

occurs without the input of energy

entropy

determines if a process will be spontaneous; measurement of the dispersal of matter and or energy

is the delta S univ positive or negative if a change is spontaneous?

POSITIVE

equation for deltaSuni

Sfinal-Sinitial

entropy of a system

deltaS=qrev/T

what is qrev also equal to?

ndeltaH

equation for entropy of an ideal gas?

deltaS=nrln(V2/V1)

if V1 is greater than V2 is this an isothermal expansion of compression?

compression

if V1 is greater than V2 is delta S positive or negative?

negative

if V2 is greater than V1 is this an isothermal expansion or compression?

expansion

if V2 is greater than V1 is delta S positive or negative?

positive

equation for entropy of an ideal gas when the temperature is reversible?

deltaS=nCmln(T2/T1)

statistical definition of entropy

S=klnW

thermal equilibrium

objects are at the same temperature which means there’s no longer an exchange of heat energy

chemical equilibrium

there is no change in the quantity of our products and reactants

gibbs free energy

relates enthalpy and entropy; measure of the spontaneity of a process

equation for gibbs free energy

deltaG=deltaH-TdeltaS

for a spontaneous process is the gibbs free energy negative or positive?

negative

do processes spontaneously move to lower or increase their free energy?

lower

exergonic

negative free energy

endergonic

positive free energy

what is the value of free energy at equilibrium?

0

what is K equal to

[products]/][reactants]

equation for deltaGrxn

-RTlnK

van’t hoff equation

lnK=-deltaH/RT+deltaS/R

what is Q?

reaction quotient; measure of a reaction’s progress towards equilibrium

if Q<K

reaction goes from left to right; decrease in reactants, increase in products

if Q>K

reaction goes from right to left; decrease in products, increase in reactants

Q=K

at equilibrium

deltaGrxn at non-standard conditions

=deltaGnotrxn+RTlnQ

Le Chatelier’s Principle

when a reaction is at equilibrium and it then perturbed in some way so as to change Q or K, the system will go in the direction to reduce that stress

what happens when we decrease the volume of a reaction

the reaction shifts to the side with fewer gas particles

what happens if we increase the volume of a reaction

the reaction shifts to the side with more moles of gas

steps to calculate equilibrium concentrations using an ICE table

1. write down a balanced equation

2. determine which way the reaction will go (compare Q to K)

3. construct ICE table

4. I(initial): concentrations or partial pressures of all the reactants at the moment they are brought together but before they have started to react

5. C(change): change in the concentrations

6. E(equilibrium): write the equilibrium concentration or partial pressure of e/ reactant

7. Plug values into the expression for K and solve for X and then solve for equilibrium concentrations of products and reactants

can your X value be higher than your initial concentration?

NO

arrhenius definition of an acid

a substance that produces H+ ions (protons) in aqueous solutions

arrhenius definition of a base

a substance that produces OH- ions (hydroxide) in aqueous solutions

Bronsted-Lowry definition of an acid and base

acid → proton donor

base → proton acceptor

strong acid

an acid that completely dissociates in water; almost every molecule or ion of a strong acid reacts to produce a hydronium ion

what determines the strength of an acid or a base?

how well it can dissociate in water

what does a one sided arrow mean?

the acid/ base fullt dissociates and the reaction is not reversible

what constant is used to measure the strength of an acid

Ka

does a large Ka mean a strong or a weak acid?

strong

does a large pKa mean a strong or a weak acid

weak

how do you find the pKa

by taking the -log(Ka)

what is pH?

a way of discussing the concentration of [H3O]+ in a solution; pH=-log[H3O+]

what is pOH?

a way of discussing the concentration of [OH-] in a solution; pOH=-log[OH-]

what does it mean if something is amphoteric

it can act as either an acid or a base

Kw

ion-product constant for water

what is Kw equal to

[Ka]x[Kb]=Kw = 1.0×10^-14

what is a spectator ion

an ion that does not participate in the chemical reaction

why are some ions spectator ions?

1. they dont have a proton

2. they don’t have a lone pair

buffers

a chemical system that resists pH changes by neutralizing added acid or base

Henderson-Hasselbach Approximation

relates the pH of a buffer at equilibrium to the initial concentrations of the buffer components (assuming x is small)

Henderson-Hasselbach Approximation Equation

pKa+log([A-] initial/[HA]initial)

relationship between pKa of the acid and the pH of the buffer when we have equal concentrations of acid and base

pH=pKa

Acid-base titration

a substance in a solution of known concentration is reacted (by careful addition of a measured volume) with another substance in a solution of unknown concentration

equivalence point

the number of moles of added titrant is equal to the number of moles of analyte

titrant

known concentration