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# THE MCAT-CHEM 6

### THERMODYNAMICS

Closed system exchange of heat and work but not matter with the surroundings
isolated system no exchange of heat, work, or matter with the surroundings
open system exchange of heat, work, and matter with the surroundings
What are the characteristics of a state function? path-independent --> only depend on final and initial states
What do state functions include? enthalpy, entropy, free energy change (delta G), and internal energy change (delta U)
Endothermic / exothermic reaction, delta H = positive / negative
What does delta H mean? change of heat content of a reaction
What is standard state? natural, lowest energy state
What is standard state for oxygen? O2
Why is bond dissociation energy positive? energy input is required to break bonds
Why is enthalpy of formation negative? energy is released when bonds are formed
Calculate bond dissociation energy. bond dissociation energy of all bonds in reactants - bond dissociation energy of all bonds in products
Calculate enthalpy of formation. enthalpy of all bonds in products - enthalpy of formation of all bonds in reactants
T / F. A change in one degree C is the same as a change in 1 K TRUE
heat capactiy the amt of heat required to raise the temp of something by one degree celsius
molar heat capacity heat capacity per mole ( Joules / mol*C)
specific heat capacity heat capacity per mass (Joules / g*C)
How many Joules of energy does it take to raise the temp. of 1 gram of water by 1 degree celsius? 4.2 J
How many joules of energy does one calorie equal? One Calorie? 4.2 J 4200 J
How many calories does one Calorie equal? 1000
What is free energy? energy available that can be converted to do work
Are all exothermic rxns spontaneous? NO --> depends on entropy delta G = delta H - T*delta S
Do spontaneous rxns happen quickly? not necessarily
Zeroth Thermodynamic law heat flows from hot objects to cold objects to achieve thermal equilibrium
If Ta = Tb, Tb = Tc, then? Ta = Tc
First Thermodynamic Law Conservation of energy --> change in total energy of a system is equal to contributions from heat and work
What does delta E equal to in thermodynamics? q + w
When is q positive? negative? -heat absorbed into system -heat leaks out of system
When is work positive? negative? -work done on system -work done by system
T / F. ALL energy is equivalent even if they are in different forms. TRUE
Second thermodynamic law universe is increasing in entropy
Why is entropy increasing? irreversibility nature of real processes
Room temperature in celsius? body temperature? 25 / 37
How to convert from celsius to fahrenheit? C * 1.8 + 32 = F
Conduction heat transfer by direct contact
Convection heat transfer by flowing current through a fluid medium
Radiation heat transfer by EM radiation through emission of photon energy (infrared range)
Can radiation occur in a vacuum? YES
heat of fusion energy input needed to melt something from solid to liquid at constant temperature
heat of vaporization energy input needed to vaporize something from liquid to gas at constant temperature
adiabatic process no heat exchange --> deltaE = W
isothermal process no change in temperature
isobaric pressure pressure is constant, W = P*deltaV
isochoric process volume is constant, W = 0
When does the q = mcdeltaT formula work? if no phase change is involved
Heat of fusion / vaporization is measured in Joules
Heat of fusion equation q = delta H (fusion) * number moles
Heat of vaporization equation q = delta H (vaporization) * number moles
At what temperature does ice melt? Water freeze 0 degrees C
At what temperature does water boil? Steam condense? 100 degrees C
A refrigerator takes in _____ and releases _____. An engine takes in ______ and releases ____. work / heat heat / work
Why does air blown from pursed lips feel cool on the skin? Expansion of a gas is an endothermic process as it hits the skin
Formula for Work with gas expansion / compression W = - P * deltaV
Forming bonds is an _____ process Breaking bonds is an ______ process. exothermic / endothermic
Expansion of a gas is _________. Compression of a gas is ________. endothermic / exothermic
Third Law of Thermodynamics entropy of a perfect crystal at 0 K is O
Relate E, q, and w. delta E = q + w
Favorable at? -S positive, H negative -S negative, H positive -S positive, H positive -S negative, H negative -all temperatures -at no temperatures -at high temperatures -at low temperatures
Rank the enthalpy changes for: melting, evaporation, sublimation sublimation > evaporation > melting
Why does a higher reaction temperature accelerate the rxn? greater KE within the reactants
After reaction completes, what then proceeds? equilibrium
S deals with ____ while G deals with _____. -entropy -whether or not rxn is spontaneous
Does Keq give any information about kinetics? NO --> only thermodynamics
Does the slow or fast step have the highest energy to get over? slow
What defines the rate of a reaction? activation energy and kinetic region
What type of diagram is activation energy read from? free energy
What does deltaGo show? free energy change when a reaction goes from standard conditions to equilibrium
Does enthalpy say anything about favorability of a reaction? NO
In an exothermic reaction, are the products lower or higher than reactants? lower
In an endothermic reaction, are the products lower or higher than the reactants? higher
Do cyclic compounds have more or less entropy than linear compounds? less --> more rigid and cannot rotate
For G and H of formation, an element in its basic form has a value of? 0
What are the diatomic gases? Fluorine, Oxygen, Nitrogen, Chlorine, Hydrogen
What are the diatomic liquids? Bromine
What are the diatomic solids? Iodine
How many moles of products do formation reactions create? one mole
In an exo rxn, are the bonds formed stronger or weaker than those broken? stronger
What are weaker bonds? On the energy diagram are they high or low? long bonds / high
Does a tertiary carbon form a stronger or weaker bond with hydrogen than a primary carbon? weaker --> carbocation stability
What is the heat capacity fo rwater 1 cal / g*K
How to find the final temp. created from mixing 2 solutions with different temperatures? mcdeltaT = - mcdeltaT
Do solids have higher or lower heat capacities than liquids? lower --> only vibrational kinetic energy
materials with high heat capacities experience smaller or greater temperature increases? smaller
Is the enthalpy of vaporization greater or less than the heat of fusion? greater
strong base + strong acid = water and neutral salt
Why must a lid be used in a calorimetry experiment? To prevent heat loss from convection and evaporation **
Is warm air less dense or more dense than cool air? less dense
What happens to an object as it radiates photon energy? object becomes cooler and molecules move less energetically
What are 2 formulas for work? W = F*delta d W = -P * delta V
What does it mean when "q" is positive vs. negative? -positive = heat flows from surroundings into system -negative = heat flows from system into surroundings
Thermodynamic Energy Equation delta E = q + w
When does work = 0? constant volume
If a precipitation reaction is favorable, then delta G =? negative
Does water or salt water have the greater heat capacity? salt water
The lower the heat capacity, the greater or less the temperature increase? greater
When something has greater heat capacity, it also has greater? kinetic energy
Created by: 507935299