Thermodynamics and Thermochemistry Flashcards
what are the types of systems and their exchanges?
open, closed, isolated
open exchanges both matter and heat. closed only exchanges heat. isolated exchanges nothing
what happens at thermal equilibrium?
all objects have same final temperature
whats the first law of thermodynamics?
total energy of isolated system conserved. E=q+w
what are the types properties?
extensive property: quantity depends on amount of material.
intensive property: doesnt depend on amount of material
state function: property doesnt depend on route taken only current state
what is internal energy? what type of property is it?
an extensive property and state function. its the sum of kinetic and potential energy of all components in system
can absolute internal energy be measured?
no but changes (delta E) can
what does the sign (positive/negative) of work tell about the volume of a gas?
positive work done means compressing ion. negative means expansion
how does heat always flow?
from warmer to cooler
what are examples of intensive properties?
temperature, density, melting/boiling point
what are examples of extensive properties?
volume, mass, energy (enthalpy)
what are examples of state function?
volume, pressure, enthalpy, entropy, speed, internal energy
what sign of heat determines each type of reaction?
positive heat is endothermic. negative heat is exothermic.
what does the sign of work tell about the temperature?
if work is positive, it is cooled. if work is negative, it is heated
if the volume of a gas doesn’t change, what can be said about work?
it is 0
what is enthalpy?
change at constant pressure
what is latent energy?
energy associated with phase change
what can be said about a exothermic process (about H)?
heat is lost. q is negative = H is negative
where does heat exchange occur in calorimeter?
only within system (calorimeter, reactants, solvent)
what is a bomb calorimeter?
best for gaseous/combustion reactions. unlike normal calorimeter, Ccal is not negligible. the experiment occurs under constant volume so Qrxn=deltaE
what is the standard enthalpy of formation?
measure of energy released/absorbed when one mole of substance is created under standard conditions from its pure element (in their reference state)
what are the steps for calorimeter calibration?
add hot water… measure T at equilibrium…. carry out chemical reaction
What are standard conditions?
298.15 K and 1atm (101.33 kPa)
what are the reference states?
stable state of an element. all are solids except for… mercury and bromine which are liquids. noble gases, hydrogen, nitrogen, oxygen, fluorine, and chlorine are gases. sometimes they are molecules: diatomic (H2, N2, O2, F2, Cl2, Br2, I2, At2, S8)
What are are allotropes? Whats the most common/stable allotrope of carbon?
solids that have more than one common structure. for carbon most stable is graphite
What can be said about an elements deltaHf at its reference state?
its 0, use table for other values
What does Hess’s law of thermochemistry state?
enthalpy change for a reaction is sum of enthalpy changes for individual steps of the reaction
What is the standard enthalpy of combustion?
enthalpy change when one mole of substance in standard state undergoes complete combustion with oxygen to form products in standard state (e.g. CO2 g and H2O l). incomplete combustion may result in CO H20 l
what is bond enthalpy?
energy req to break 1 mole of a specific type of bond between two atoms. (all reactants and products must be gas). bond breaking is always endothermic therefore positive value
what is total bond enthalpy?
energy req to break all bonds in 1 mole of a gaseous molecule to produce gas-phase atoms
whats the formula for the H reaction that uses total bond enthalpy?
Reactants - product (bonds broken - bonds formed)
what determines spontaneity?
free energy (determined by enthalpy, entropy, and temperature)
what is entropy? what can increase it?
dispersion of energy. measure of disorder. entropy change is a state function. the process of increasing S is spontaneous. temperature and phase changes can increase entropy
what does the 2nd law of thermodynamics state?
total entropy of isolated system can never decrease. every spontaneous process increases entropy of universe.
what does the 3rd law of thermodynamics state?
entropy of a perfect crystal is zero at 0k.
what can be said about gas molecules and entropy?
in a reaction, if the product has more gas molecules it has positive entropy therefore non-spontaneous
what is free energy? relation to spontaneity?
deltaG. it examines system and related enthalpy and entropy changes. deltaG=deltaH-TdeltaS. if deltaG is negative it is spontaneous, 0=equilibrium.
what drives a spontaneous process?
If H & G have a diff sign from S, reaction is enthalpically and entropically driven. If H & S is negative: enthalpically driven if spontaneous. If H & S positive, entropically driven if spontaneous
what are some reactions that are entropically driven?
fusion and vaporization. at melting pt G=0 at equilibrium
what are the conditions for standard free energy change?
298 K and 1atm pressure(gases) / 1M concentration(solution)
what is standard free energy of formation?
deltaGf=0 (at standard state). free energy when one mole of a substance in its standard state is made from elements in their standard states. used w hess law
