Thermodynamics and Thermochemistry

Question 1

what are the types of systems and their exchanges?

Answer 1

open, closed, isolated

open exchanges both matter and heat. closed only exchanges heat. isolated exchanges nothing

Question 2

what happens at thermal equilibrium?

Answer 2

all objects have same final temperature

Question 3

whats the first law of thermodynamics?

Answer 3

total energy of isolated system conserved. E=q+w

Question 4

what are the types properties?

Answer 4

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

Question 5

what is internal energy? what type of property is it?

Answer 5

an extensive property and state function. its the sum of kinetic and potential energy of all components in system

Question 6

can absolute internal energy be measured?

Answer 6

no but changes (delta E) can

Question 7

what does the sign (positive/negative) of work tell about the volume of a gas?

Answer 7

positive work done means compressing ion. negative means expansion

Question 8

how does heat always flow?

Answer 8

from warmer to cooler

Question 9

what are examples of intensive properties?

Answer 9

temperature, density, melting/boiling point

Question 10

what are examples of extensive properties?

Answer 10

volume, mass, energy (enthalpy)

Question 11

what are examples of state function?

Answer 11

volume, pressure, enthalpy, entropy, speed, internal energy

Question 12

what sign of heat determines each type of reaction?

Answer 12

positive heat is endothermic. negative heat is exothermic.

Question 13

what does the sign of work tell about the temperature?

Answer 13

if work is positive, it is cooled. if work is negative, it is heated

Question 14

if the volume of a gas doesn’t change, what can be said about work?

Answer 14

it is 0

Question 15

what is enthalpy?

Answer 15

change at constant pressure

Question 16

what is latent energy?

Answer 16

energy associated with phase change

Question 17

what can be said about a exothermic process (about H)?

Answer 17

heat is lost. q is negative = H is negative

Question 18

where does heat exchange occur in calorimeter?

Answer 18

only within system (calorimeter, reactants, solvent)

Question 19

what is a bomb calorimeter?

Answer 19

best for gaseous/combustion reactions. unlike normal calorimeter, Ccal is not negligible. the experiment occurs under constant volume so Qrxn=deltaE

Question 20

what is the standard enthalpy of formation?

Answer 20

measure of energy released/absorbed when one mole of substance is created under standard conditions from its pure element (in their reference state)

Question 21

what are the steps for calorimeter calibration?

Answer 21

add hot water… measure T at equilibrium…. carry out chemical reaction

Question 22

What are standard conditions?

Answer 22

298.15 K and 1atm (101.33 kPa)

Question 23

what are the reference states?

Answer 23

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)

Question 24

What are are allotropes? Whats the most common/stable allotrope of carbon?

Answer 24

solids that have more than one common structure. for carbon most stable is graphite

Question 25

What can be said about an elements deltaHf at its reference state?

Answer 25

its 0, use table for other values

Question 26

What does Hess's law of thermochemistry state?

Answer 26

enthalpy change for a reaction is sum of enthalpy changes for individual steps of the reaction

Question 27

What is the standard enthalpy of combustion?

Answer 27

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

Question 28

what is bond enthalpy?

Answer 28

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

Question 29

what is total bond enthalpy?

Answer 29

energy req to break all bonds in 1 mole of a gaseous molecule to produce gas-phase atoms

Question 30

whats the formula for the H reaction that uses total bond enthalpy?

Answer 30

Reactants - product (bonds broken - bonds formed)

Question 31

what determines spontaneity?

Answer 31

free energy (determined by enthalpy, entropy, and temperature)

Question 32

what is entropy? what can increase it?

Answer 32

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

Question 33

what does the 2nd law of thermodynamics state?

Answer 33

total entropy of isolated system can never decrease. every spontaneous process increases entropy of universe.

Question 34

what does the 3rd law of thermodynamics state?

Answer 34

entropy of a perfect crystal is zero at 0k.

Question 35

what can be said about gas molecules and entropy?

Answer 35

in a reaction, if the product has more gas molecules it has positive entropy therefore non-spontaneous

Question 36

what is free energy? relation to spontaneity?

Answer 36

deltaG. it examines system and related enthalpy and entropy changes. deltaG=deltaH-TdeltaS. if deltaG is negative it is spontaneous, 0=equilibrium.

Question 37

what drives a spontaneous process?

Answer 37

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

Question 38

what are some reactions that are entropically driven?

Answer 38

fusion and vaporization. at melting pt G=0 at equilibrium

Question 39

what are the conditions for standard free energy change?

Answer 39

298 K and 1atm pressure(gases) / 1M concentration(solution)

Question 40

what is standard free energy of formation?

Answer 40

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