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chem 1302 > Thermodynamics and Thermochemistry > Flashcards

Thermodynamics and Thermochemistry Flashcards

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1
Q

what are the types of systems and their exchanges?

A

open, closed, isolated

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

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2
Q

what happens at thermal equilibrium?

A

all objects have same final temperature

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3
Q

whats the first law of thermodynamics?

A

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

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4
Q

what are the types properties?

A

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

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5
Q

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

A

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

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6
Q

can absolute internal energy be measured?

A

no but changes (delta E) can

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7
Q

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

A

positive work done means compressing ion. negative means expansion

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8
Q

how does heat always flow?

A

from warmer to cooler

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9
Q

what are examples of intensive properties?

A

temperature, density, melting/boiling point

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10
Q

what are examples of extensive properties?

A

volume, mass, energy (enthalpy)

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11
Q

what are examples of state function?

A

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

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12
Q

what sign of heat determines each type of reaction?

A

positive heat is endothermic. negative heat is exothermic.

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13
Q

what does the sign of work tell about the temperature?

A

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

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14
Q

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

A

it is 0

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15
Q

what is enthalpy?

A

change at constant pressure

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16
Q

what is latent energy?

A

energy associated with phase change

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17
Q

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

A

heat is lost. q is negative = H is negative

18
Q

where does heat exchange occur in calorimeter?

A

only within system (calorimeter, reactants, solvent)

19
Q

what is a bomb calorimeter?

A

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

20
Q

what is the standard enthalpy of formation?

A

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

21
Q

what are the steps for calorimeter calibration?

A

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

22
Q

What are standard conditions?

A

298.15 K and 1atm (101.33 kPa)

23
Q

what are the reference states?

A

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)

24
Q

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

A

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

25
Q

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

A

its 0, use table for other values

26
Q

What does Hess’s law of thermochemistry state?

A

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

27
Q

What is the standard enthalpy of combustion?

A

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

28
Q

what is bond enthalpy?

A

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

29
Q

what is total bond enthalpy?

A

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

30
Q

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

A

Reactants - product (bonds broken - bonds formed)

31
Q

what determines spontaneity?

A

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

32
Q

what is entropy? what can increase it?

A

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

33
Q

what does the 2nd law of thermodynamics state?

A

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

34
Q

what does the 3rd law of thermodynamics state?

A

entropy of a perfect crystal is zero at 0k.

35
Q

what can be said about gas molecules and entropy?

A

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

36
Q

what is free energy? relation to spontaneity?

A

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

37
Q

what drives a spontaneous process?

A

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

38
Q

what are some reactions that are entropically driven?

A

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

39
Q

what are the conditions for standard free energy change?

A

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

40
Q

what is standard free energy of formation?

A

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

chem 1302 (3 decks)

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