Chemistry 2

Question 1

Common forms of ΔH

• Define ΔH_formation
  
  • _​If number is NEGATIVE, formation of the cpd is an ______ process
  • If number is POSITIVE, formation of the cpd is an _____ process

Answer 1

ΔH_formation

• The enthalpy value for the formation of a compound
  
  • …from its elements in their standard states

If ΔH_formation value is NEGATIVE:

• Formation of the cpd is an EXOthermic process

If ΔH_formation value is POSITIVE:

• Formation of the cpd is an ENDOthermic process

Question 2

∆Hvaporization definition

Answer 2

enthalpy value associated with phase change from liquid to gas(therefore, ∆Hcondensation is the same value, just with a reverse sign)

Question 3

Common forms of ΔH

• Calculating for “ΔH_rxn“

…Using Bond Dissociation Energies (BDE’s)

• How do you solve for ΔH_rxn?
  
  • Wrt signs (+/-), what do you do if a bond is BROKEN? If a bond is FORMED?
  • What last thing do you need to remember to do before you’re done solving for ΔH_rxn?

Answer 3

Calculating ΔHRXN Using Bond Energies:

This is not quite as common on the MCAT as the method of adding reactions (but it is a bit more intuitive in our opinion)

STEPS:

To do so, simply add up the BDE’s of all of the products and reactants

• If a bond is BROKEN during the reaction:
  
  • Energy is REQUIRED
    
    • ∴ the BDE should be given a POSITIVE sign
• If a bond is FORMED during the reaction:
  
  • Energy is RELEASED
    
    • ∴ the BDE should be given a NEGATIVE sign

Once again, multiply all bond energy values by their coefficients in the balanced equation

Question 4

The ln of and positive (+) numer LESS than 1 is?

Answer 4

negative (-)

Question 5

How do you solve for ΔH using a BOMB Calorimeter?

• What DOES and DOESNT solving for Bomb Calorimeters give us?

Answer 5

Solve using q=mc ∆T

DOES give:

• change in internal energy (∆U or ∆E)

DOESNT give:

• a negative ∆H
• bomb calorimeter is at ~V, in a sealed steel container*

Question 6

Rate Order Graphs:Will only be linear when? (2)

Answer 6

1) When rxn only has 1 reactant, or2) when it is part of a multiple reactant rxn where rate is independent of ALL other reactants (basically, when the other reactant is zeroth order or is in excess)

Question 7

What is a Black Body Radiator?

Answer 7

Theoretically perfect body that absorbs ALL energy that hits it, and then re-emits 100% of the energy absorbed

Question 8

What formula relates the Keq to Gibbs Free energy? (2 versions)

Answer 8

∆G˚=-RTlnKeqORKeq=e^(-∆G/RT)

Question 9

∆G (-) means?

Answer 9

energy must be added to rxn (i.e. heat must be added to system) to make it proceed

Question 10

Define the ZEROTH LAW of Thermodynamics

Answer 10

• If object A is in thermal equilibrium with object B
• And object C is in thermal equilib with object B

…then object A and object C are ALSO in thermal equilibrium!

Question 11

Calculating ∆Hrxn using BDE’s

Answer 11

add up BDE’s in products & reactants-bond broken during rxn= energy REQUIRED, BDE has (+) sign-bond formed as a result of rxn= energy RELEASED, BDE has a (-) sign

Question 12

Acid-Base Chemistry

• Describe a Bronsted-Lowry Acid & Base

HINT: Black L.A.P.D

Answer 12

Acids

• DONATE protons (H + )

Bases

• ACCEPT protons (H + )

“B.L.A.P.D”

BLACK L.A.P.D

Question 13

If Keq > 1, rxn will be…?(if we are starting at standard conditions)

Answer 13

SPONTANEOUS!

Question 14

On a pressure vs. volume graph:

• Where is PV work?

Answer 14

The area UNDER the curve

Question 15

How to calculate ORDER of each reactant (using experimental data)

Answer 15

1) Find 2 steps where [reac] in question changed, but ALL OTHERS DID NOT2) Note the factor by which [reac] changed3) note the factor by which RATE changed across those same 2 trials4) Use this to figure out X^Y=Z

Question 16

Thermodynamics

• How is “WORK”defined inCHEMISTRY?

Answer 16

Work=

A change in VOLUME

• …at a constant ~P

Question 17

How will the following affect rxn rate?

increasing energy of transition state

Answer 17

DECREASE rate

because it increases E_a

Question 18

Bond broken during rxn=energy ___

Answer 18

required

Question 19

Heat capacity formula

Answer 19

C=q/∆T

Question 20

How will the following affect rxn rate?

increase [reactants]

Answer 20

increase rate

Question 21

Differentiate heat capacity “C” and specific heat capacity “c”

Answer 21

Heat capacity is for a system (ex: solution, container holding sol’n, etc.)Specific heat capacity describes energy absorption for ONE individual substance ONLY!

Question 22

What should you think of (and mentally replace!) whenever you see the word “temperature?”

Answer 22

temperature=av. KE of molecules

Question 23

PV Work

• Formula=?
• What do you need for in order to see PV work?
• What is a dead giveaway PV work has been done?

Answer 23

PV Work =P∆V

Needs ~P

Change in Volume is a dead giveaway!!

Question 24

if slow step is 2nd, what happens wrt the rate law?

Answer 24

rate law=rate law of the slow stepslow step will include an intermediate as of the reactants

Question 25

Bond formed as result of rxn=energy \_\_\_

Answer 25

released

Question 26

∆Hfusion definition

Answer 26

enthalpy value associated with phase change from liquid to solid (sign reverses for ∆Hmelting)

Question 27

Entropy, ∆S **POSITIVE** ∆S means? * _______ randomness, ____ energy available to do work

Answer 27

* **INCREASED** randomness * **MORE** energy available to do work

Question 28

A reaction with a **HIGHER** **∆S** ## Footnote *is **more** likely to?*

Answer 28

Happen **SPONTANEOUSLY!**

Question 29

If 2 objects are in thermal equilibrium, by definition they have what?

Answer 29

The SAME TEMP!

Question 30

How will the following affect rxn rate? ## Footnote **increasing [catalyst]**

Answer 30

**increase** rate

Question 31

Acid-Base Chemistry * What are 2 **COMMON** examples of **Lewis Acids?** (LAEPA) THINK: What 2 things are very **likely** **to** **accept** an electron pair?

Answer 31

**AlCl₃** **BF₃**

Question 32

*What is the **SPECIFIC HEAT** of **H₂O?***

Answer 32

_Specific Heat of Water=_ **1.0 cal/g˚C** OR **4.18 J/g˚C**

Question 33

Define the **FIRST** **LAW** of thermodynamics

Answer 33

* Energy cannot be **created** nor **destroyed**

Question 34

Thermodynamic Formula

Answer 34

∆G=∆H-T∆S

Question 35

∆Hrxn definitionHow do you solve for it? (1 step, 2 things to remember to do)

Answer 35

enthalpy change for a rxn. -Add together enthalpy change values from the table (given) that, when added, produce net rxn for which you are calculating ∆Hrxn-REMEMBER: if rxn proceeds in opposite direction as it would in the net rxn, change its sign! -REMEMBER: You need to multiply the value given in the table by the coefficient in the balanced net rxn (like...if ∆H value from table for H20 is 1.5 but you have 2 moles of water, multiply 1.5 x 2=3)

Question 36

When comparing trials to write a rate law for a reactant, what should you look for?

Answer 36

Find 2 trials where []'s of reactant A changes, but everything else (like [] of reactant B and temperature) stays the same. Something with the same conditions!

Question 37

Rate Order graphs: first order

Answer 37

ln [A] vs time is linear with slope= -k

Question 38

Define heat capacity

Answer 38

amount of energy (in joules or calories) a system must absorb to give a unit change in temperature

Question 39

Enthalpy * Define "**Standard State**" * What values do you need to have memorized for Standard State? * What should you be careful not to mix it up with?

Answer 39

**_​STANDARD STATE_** is a set of conditions set as a **REFERENCE POINT** for measuring: **∆H, ∆G, and ∆S** * Do **NOT** memorize **ANY** values for Standard State! * because they can be **different** for **different** tables _*Don't mix **Standard State** up with **​STP!***_ STP=**S**tandard **T**emperature & **P**ressure **​** **​**

Question 40

Relationship b/t enzymes & catalysts

Answer 40

Enzyme=biological catalystALL enzymes are catalysts, but not all catalysts are enzymes

Question 41

_**ZEROTH** Law of Thermodynamics (A=B, B=C, ∴ A=C)_ * What is the equation that shows the direct relationship b/t **TEMP** and **KE**? HINT: It uses Boltzmann's Constant, "**k_B"**

Answer 41

**_KE_=**(3/2)**k_B_T_** "OSD"

Question 42

The First Law of Thermodynamics _2 ways to define:_ 1. The total energy of an **isolated** system is always **constant** 2. The energy change in a **closed** system is equal to the heat **absorbed** **by** that system plus any work **done on** that system by its surroundings * **∆E = q + w** *​How do both of these definitions of the First Law essentially say the **SAME THING?***

Answer 42

**BASICALLY**: What we consider to be "**The System**" & "**The Surroundings"** is all **RELATIVE!!** * An isolated system is a system for which neither mass nor energy can be exchanged with the surroundings * A closed system is a system that can exchange energy with its surroundings but not mass. Definition 2 treats the system and its surroundings separately * It is overtly stated that energy transfer is occurring between the system and the surroundings (i.e., work is being done on the system by the surroundings and/or heat is being added to the system from its surroundings) * The total energy change of the system in case 2 would therefore be the sum of the energy absorbed and the work done on the system (∆E = q + w) * However, if we defined "**the system**" as BOTH the system receiving the heat/work AND its surroundings, we would then have an isolated system * The entire isolated system would **not** change in energy—**which is exactly what definition 1 implies** * What were formerly considered the “system” and the “surroundings” in definition 2 are now just parts of the “system” as defined for definition 1 * Therefore, heat or work can be transferred back and forth between parts of the system and the total energy of the entire isolated system would not change * To further illustrate, let’s say that 10J of heat were transferred to the system and 10J of work were also done on the system by the surroundings * According to definition 2, ∆E = 10J + 10J = 20J * According to definition 1, ∆E_system = 10J + 10J = 20J and ∆E_surroundings = -10J + (-10J) = -20J * Therefore ∆E_{isolated system} = 20J – 20J = 0

Question 43

When you see "**ENTHALPY (ΔH)**," ## Footnote *THINK: ?*

Answer 43

The **ENERGY CONTAINED** ## Footnote **_WITHIN_ CHEMICAL BONDS**

Question 44

∆Hsol'n definition

Answer 44

enthalpy value associated with dissolution of a species into a solution

Question 45

Convection, Conduction, & Radiation * A pan of water is placed upon an electric heating element on a stove * Describe all types of heat exchange expected to occur in this scenario

Answer 45

Question 46

What do exponents in a rate law represent?

Answer 46

the "order" of each reactant

Question 47

High (+) BDE means the cpd is very \_\_\_

Answer 47

stable

Question 48

Entropy, ∆S * _How would the following affect **ENERGY?**_ As a reaction proceeds, its **∆S** **INCREASES** * **​**i.e., becomes more **DIS**ordered

Answer 48

Energy will be **RELEASED** * ∴ **MORE** energy will be **available** to do **work!** * In short: It's **_FAVORABLE_***

Question 49

the word "decomposition" tells us what?

Answer 49

we are going from ONE species to 2+ species (∆S is positive)

Question 50

What are the 3 types of heat exchange?

Answer 50

1) Convection2) Radiation3) Conduction

Question 51

Think of ∆H as...units?

Answer 51

energy contained w/in chemical bondsunit= Joules

Question 52

How will the following affect rxn rate? ## Footnote **increase [products]**

Answer 52

**NO** effect

Question 53

Entropy, ΔS **_INCREASES_** when there is an **INCREASE** **IN:** *(**4 things** can increase entropy)* One of these 4 carries a **CAVEAT**! HINT: gas

Answer 53

**_Entropy increases with:_** 1) Increased **number** of: * items/particles/etc. _Caveat_: *The number of **moles of GAS _TRUMPS_** the number of moles of species in any **other** phase!* * Thus, **even if** a reaction turns **2** **moles** of reactants into **1** **mole** of product, if that one mole of product is a **GAS** and the reactants are **NOT:** * Entropy has increased * ΔS will therefore be **positive** 2) Increased **VOLUME** 3) Increased **TEMPERATURE** 4) Increased **DISORDER** or **COMPEXITY** * Increased "**Order**" * a crystal (highly ordered) is changed to an amorphous material (highly **dis**ordered) * Increased "**Complexity**" * S is greater for **C₂H₆** than for **CH₄**

Question 54

Large (-) ∆Hformation means what? (2)

Answer 54

Energy released when bonds are formed is very highcompound is very stable

Question 55

If a graph for a reactant is linear at:[A] vs. time, slope=-kit must be? What if it isnt linear?

Answer 55

Zeroth order not linear=not zeroth order, but it could be first or second, etc

Question 56

More unstable cpds: -∆Hcombustion?

Answer 56

have a HIGHER ∆Hcombustion, release MORE energy when reacted with O2

Question 57

Isobaric definition

Answer 57

~P

Question 58

[OH][H]What increases in [] when you INCREASE pH?

Answer 58

[OH]

Question 59

Think of Gibbs Free Energy, ∆G, as...

Answer 59

the amount of "free" or "useful" energy available to do work (\*\*Note\*\*doesnt include pv work)

Question 60

* Name the 2 kinds of **calorimeters** * What are their distinguishable properties? * HINT: What is *constant* in each type?

Answer 60

1. **COFFEE CUP** Calorimeters * ~P 2. **BOMB** calorimeters * ~V

Question 61

Calorimeters * Which type of calorimeter allows for **PV WORK?** * Why?

Answer 61

**COFFEE CUP** Calorimeters! * because it's **constant** **pressure** * Top of cup is **covered** by insulated cork "**stopper**"*

Question 62

Light colors radiate and absorb \_\_\_dark colors radiate and absorb \_\_\_

Answer 62

Light: absorb lessDark: absorb more

Question 63

When values are given for standard state conditions, what thingy is added?

Answer 63

superscript is added --\> ∆H˚ "not"

Question 64

Heat Exchange * Define **RADIATION** Give an example

Answer 64

**Electromagnetic waves** emitted from **hot** body into surrounding **environment** * ex: a black car on a hot day emits heat

Question 65

When a solute is mixed in solution, ∆S is always \_\_\_. Why?

Answer 65

is always (+)something becomes more disordered dissolved in a solution

Question 66

Entropy, ∆S a **NEGATIVE** ∆S means? * _______ randomness, ____ energy available to do work

Answer 66

* **LESS** randomness * **LESS** energy available to do work

Question 67

Give an example of ~V heat capacity

Answer 67

system confined by rigid walls

Question 68

Which thermodynamic elements are "NON-SPONTANEOUS" or "UNFAVORABLE?"

Answer 68

∆G is (+)∆S is (-)∆H is (+)

Question 69

When writing **RATE LAWS,** what 2 things must you **assume**?

Answer 69

1) Assume reactions only proceed **FORWARD** * **ignore** reverse rxn 2) Only consider the **first few seconds** of the reaction * when theres a **high []** of: * **each** reactant and * **catalysts** (enzymes) present

Question 70

∆Hformation definitionExothermic=?Endothermic=?

Answer 70

enthalpy value for formation of a cpd from its elements in their natural stateExothermic is (-)Endothermic is (+)

Question 71

Do catalysts increase % yield?

Answer 71

NOPE!!

Question 72

Heat Exchange * Define **CONVECTION** What are 2 common examples?

Answer 72

***Hotter** sections of fluid **rise**, **cooler** portions **sink*** _Examples_: 1. Air currents 2. Convection currents (El Nino)

Question 73

Rate Order graphs: Zeroth order

Answer 73

[A] vs time is linear with slope= -k

Question 74

If a graph for a reactant is linear at:ln[A] vs. time, slope=-kit must be? What if it isnt linear?

Answer 74

must be 1st ordernot linear= not first order. could still be 0th or 2nd order

Question 75

# Define "**kinetics**" How is it measured?

Answer 75

study of reaction **RATE** * Measured in terms of how fast **REACTANTS** **DISAPPEAR** * by tracking **changes in []** of reactants

Question 76

When heat enters into a system, if the system is capable of volume change, heat can either...

Answer 76

Do PV workIncrease temperature (Av KE of molecules)or Both

Question 77

What DO catalysts affect? What DONT they affect?

Answer 77

DO affect rate (by lowering Ea)DONT affect Keq, ∆H, ∆S, ∆G, or any other thermodynamic properties

Question 78

in a 2-step rxn, does the yield of the first rxn affect the Keq of the second?

Answer 78

NOPERS

Question 79

Entropy increases with increasing...

Answer 79

number of moleculestemperaturevolumemoles of gas

Question 80

How to write rate law for a catalyzed rxn

Answer 80

write rate law in same way as normal, w/ [catalyst] added in as a reactant

Question 81

Collisions cause?

Answer 81

reactions!

Question 82

Slow step=?

Answer 82

rate-determining step

Question 83

How will the following affect rxn rate? ## Footnote **increase temp**

Answer 83

**increase** rate

Question 84

If a graph for a reactant is linear at:1/[A] vs time, slope=-kit must be? what if it isnt linear?

Answer 84

it must be 2nd ordernot linear=not 2nd order. could still be 1st or 0th

Question 85

Isothermal definition

Answer 85

~T (~av. KE of molecules)aka NO HEAT EXCHANGE

Question 86

∆G (+) means?

Answer 86

Energy is available and the system CAN do work

Question 87

is heat capacity greater for ~V or ~P?

Answer 87

For ~P, because it CAN do pv work as well as temperature work (therefore has more "capacity" that a system with ~V)

Question 88

How will the following affect rxn rate? increasing **energy** of reactants

Answer 88

**increase** rate * increasing energy of reactants brings it **closer** to the Ea * makes it easier to get over the "hill"

Question 89

When calculating ∆Hrxn, what do you need to remember with regards to signs?

Answer 89

bonds FORMED= energy released (-)bonds BROKEN= energy req'd (+)

Question 90

If, during a rxn, something happens and the Temp increases as a result, what must ∆H be?

Answer 90

(-) aka exothermic

Question 91

Common forms of ΔH * Define **"ΔH_combustion"** * **​**What does a **HIGH** heat of combustion mean wrt a molecule's **stability**?

Answer 91

**_ΔH_combustion_** * The enthalpy value for the **combustion** of a compound with O₂ * ...to form CO₂ and water **\_\_\_\_+ O₂⇒CO₂+ H₂O** A **HIGH** heat of combustion is associated with: * an **UN**stable molecule * ∴ a **LOW** heat of combustion means* * the molecule is more **stable***

Question 92

Calculating E˚ for electrochemical rxns

Answer 92

add together 1/2 rxns, but when calculating E˚, do NOT multiply by coefficients in balanced rxn (UNlike when you calculate ∆Hrxn by adding then multiplying BDE values by the coefficients)

Question 93

pH scale * All equilibrium constants (Keq, Ka, Kb. Kw or Ksp) are written via the ___ of ____ \_\_\_\_\_\_, with \_\_\_\_s and \_\_\_\_s **OMITTED**

Answer 93

All equilibrium constants (**K_eq, K_a, K_b K_w or K_sp**): * are written via the **_LAW of MASS ACTION_** * with **PURE** **liquids** (l) and **solids** (s) omitted*

Question 94

How is the sign of work determined in CHEMISTRY?

Answer 94

Work done ON system= positiveWork done BY system=Negative

Question 95

What should you remember for the MCAT about thermal equilibrium?

Answer 95

Everything TENDS TO move towards thermal equilibrium with everything else. -objects with higher temperatures will always equilibrate over time with their surroundings, including other objects with which they are in contact

Question 96

1˚ C= ___ Kelvin

Answer 96

274 K

Question 97

Give an example of ~P heat capacity

Answer 97

water in a beaker (open to the atmosphere)

Question 98

Common forms of ΔH * Calculating for "ΔH_rxn" * What 2 things do you **ALWAYS** need to remember to look out for when solving for ΔH_rxn? *Which of these things should you **IGNORE** when calculating for **E°** in _electrochemical_ reactions?*

Answer 98

When calculating for ΔH_rxn, **always** be cognizant of: 1. **Multiply** by the coefficients in balanced equation 2. **Change** the sign! (Depending on direction of the reaction) Solving for ΔH_rxn and E° is done in almost an **IDENTICAL** way! (Adding things together) **BUT!!!** _When calculating **E°:**_ * You **DO** **NOT** multiply by the coefficients in the balanced equation * (You **DO** change the sign if the* * half-reaction is reversed, however)*

Question 99

Catalyst definition

Answer 99

increases rxn rate w/o being consumed in the process

Question 100

∆E=?

Answer 100

q+W

Question 101

The First Law of Thermodynamics * What are the **two** common ways to **DEFINE** the First Law? HINT: Has to do with energy in both **isolated** & **closed** systems

Answer 101

1. The total energy of an **isolated** system: * is always **constant** 2. The energy change in a **closed** system: * is equal to the heat **absorbed** **BY** that system plus * any work **done** **ON** that system by its surroundings ## Footnote **∆E = q + w**

Question 102

_**ZEROTH** Law of Thermodynamics (A=B, B=C, ∴ A=C)_ * If two objects are in **THERMAL** equilibrium, by definition they have the same \_\_\_\_\_\_

Answer 102

* Same **TEMPERATURE** *

Question 103

Thermodynamics * How is **"****WORK"**defined in**PHYSICS?**

Answer 103

Work= **Energy transfer** via a **force**

Question 104

When the MCAT tests **LEWIS** acids or bases, they always specifically label them **as such** * Otherwise, when you see “acid” on the MCAT, think of ____ \_\_\_\_\_definition * In other words, think of....? * What about the "**Arrhenius"** definition?

Answer 104

* Otherwise, when you see “acid” on the MCAT, think of the **Bronsted-Lowry** definition * In other words, think of **species that donate an acidic hydrogen** * ​The **Arrhenius** definition is oversimplified and **rarely** seen on the MCAT

Question 105

Anything to the zeroth power is equal to?

Answer 105

1

Question 106

**Thermodynamics** includes what 4 things?

Answer 106

1. ΔG 2. ΔH 3. ΔS 4. K_eq

Question 107

Rate Order graphs: Second order

Answer 107

1/[A] vs time is linear, slope = k

Question 108

∆G=-RTlnKeqWhat do you need to remember about this formula?

Answer 108

This formula helps find sign of ∆Gremember: ln of a (+) that is 1 is positive\*\*remember the (-) sign in front of RT! If (lnKeq) is positive, that will turn it negative. Negative x positive=negative, therefore ∆G will be (-), & vice versa

Question 109

Entropy, ∆S _How would the following affect **ENERGY** being released/required?_ * As a rxn proceeds, if ∆S **DECREASES** * i.e., it becomes more **ORDERED**

Answer 109

* Energy would be **REQUIRED** * to create the increased **orderliness** ...and there'll be **exactly** that much **LESS** energy available to do work! *In short: it's **_UNFAVORABLE_***

Question 110

How will the following affect rxn rate? ## Footnote **increase E_a**

Answer 110

**decrease** rate

Question 111

If slow step is 1st, what can you do wrt the rate law?

Answer 111

the rate law can be written as if it were only 1 step

Question 112

What are 2 ways to define the first law of thermodynamics?

Answer 112

1) total energy of an isolated system is constant2) Total energy in a closed system (energy can leave, mass can't) is equal to the heat,q, absorbed by that system PLUS and work done on that system by its surroundings

Question 113

Acid-Base Chemistry * Describe a **LEWIS** Acid & Base ***"La E.P.A"*** *(Environmental Protection Agency **en español**)*

Answer 113

Acids * **Accept** a **PAIR OF ELECTRONS** ***L.A.E.P.A*** Bases * **Donate** a pair of electrons

Question 114

How is the sign (+/-) defined in PHYSICS when it comes to **WORK?** **HINT:** Think of the formula for work

Answer 114

* When force & displacement are in **same** direction (ie lifting a box) * **work is (+)** * When force & displacement are in **opposite** direction (ie lowering a box) * **work is (-)**

Question 115

If Keq

Answer 115

NON-spontaneous∆G˚ is (-)

Question 116

What does Keq=1 mean?

Answer 116

rxn is at equilibrium∆G˚=0

Question 117

For ∆H rxn, if you're given an ∆H value of +1.5, but your water is a reactant instead of a product, what do you do?

Answer 117

Reverse the sign to (-)

Question 118

Heat Capacity, **C=q / ΔT** * For the **SAME** **SYSTEM**, which heat capacity will be greater? * The constant **volume** heat capacity or the constant **pressure** heat capacity?

Answer 118

_*CONSTANT **PRESSURE***_ If the **VOLUME** is held constant: * **100%** of the energy added will go toward an increase in **temperature** If the **PRESSURE** is held constant: * the volume can still change and therefore some of the added heat will go toward pv work * If we think of heat capacity as “the amount of energy we can add **before** **the system increases by one temperature unit**,” it is fairly easy to see that the system *_capable of pv work_* will be able to absorb **MORE** heat before increasing by one degree Celsius or Kelvin *_REAL-LIFE EXAMPLE:_* * It is much like asking how many gallons of water can be added to Tank A vs. Tank B? * Tank A and Tank B are **both** 5-gallon tanks * ...but Tank B is connected via a hose to a **reserve** tank that holds **2** gallons * So, you can add **5 gallons** to Tank A before it is “full” (analogous to a one unit increase in temperature) * However, you can add **7 gallons** to Tank B before it is full (**reserve tank** = **pv work**) * We would therefore say that Tank B has the higher “water capacity” in terms of our analogy *This indicates that the **constant PRESSURE** heat capacity (allows for pv work; i.e., includes the 2-gallon reserve tank) will **always** be more than the constant volume heat capacity (does not allow for pv work; i.e., no reserve tank) for the same system*

Question 119

Watts is the same as?

Answer 119

Joules per second

Question 120

Elements in their elemental state have ∆H˚formation of?

Answer 120

ZERO(no ∆ in H needed to create THEMSELVES)

Question 121

Define the **THIRD LAW** of Thermodynamics

Answer 121

Pure **crystalline** substances at **absolute zero** ...have a **∆S of 0**

Question 122

# Define "**Entropy (∆S)**" * What are its **units**?

Answer 122

**_ENTROPY_** *a measure of **DISORDER** in a system* units=**Joules/K**

Question 123

Think of "**RATE**" as...(3 parts)

Answer 123

1. a function of **how fast** the reactant molecules are moving 2. how much **KE** they have 3. **height of E_a "hill"** * that must be overcome to form products

Question 124

∆S increases with? (4, plus 1 caveat)

Answer 124

1) increased # of items/particles/molecules\*\*CAVEAT: # moles gas trumps # moles in other phases (cause gas is VERY disordered)...2 mol react with 1 mol (g) product=Positive ∆S2) Increased Volume3) Increased temp (av. KE of molecules)4) Increased DISORDER (ex: amorphous struc more disordered than crystalline) and COMPLEXITY (ex: C2H6 has greated ∆S than CH4)

Question 125

When is heat ,q, added exactly proportional to the increase in temperature? Why?

Answer 125

When system is at ~VNo PV work gets done--it 100% of energy added goes towards increasing temperature

Question 126

Heat Exchange * Define **CONDUCTION** Give an example What thing is heat conduction **analogous** to?

Answer 126

**CONDUCTION:** Molecular collisions **carry hea**t along a **current** * ex: pot of boiling water * Heat conduction is analogous to* ***current flow through a wire***

Question 127

What do you do to find the "overall order" of a rxn?

Answer 127

Add together the exponents in the rate law

Question 128

**_ZEROTH_** _Law of Thermodynamics (A=B, B=C, ∴ A=C)_ For the MCAT, just remember this: * "\_\_\_\_\_\_\_ tends to move towards ____ \_\_\_\_\_\_* * with _____ \_\_\_\_\_"*

Answer 128

**EVERYTHING** tends to move towards **THERMAL EQUILIBRIUM** with **EVERYTHING ELSE**

Question 129

∆Hcombustion definitionHigh ∆Hcombustion means what?

Answer 129

enthalpy value for combustion of a cpd w/ O2 to form water and CO2High ∆Hcomb. value=UNSTABLE molecule(low ∆Hcomb.value=stable)

Question 130

Rate Law equation:X^Y=Z What do X, Y, and Z represent?

Answer 130

X=factor by which [reac] changedY=order of reactantZ=factor by which the rate changed (across the same 2 trials)

Question 131

What thermodynamic properties are"SPONTANEOUS?" or "FAVORABLE?"

Answer 131

∆G is (-)∆S is (+)∆H is (-)

Question 132

Specific heat capacity definition

Answer 132

describes energy absorption for ONE individual substance

Question 133

Difference b/t spectator ion and catalyst

Answer 133

-spectator ion: no effect, do NOT participate in rxn-catalyst: decreases Ea, increases rate. NOT consumed in rxn (makes it through the rxn without changing. Same among products as it is among reactants)

Question 134

Common forms of ΔH * Define **ΔH_rxn** * How do you usually **calculate** a ΔH_rxn? * What do you add to get the ΔH_rxn? * What 2 things must you remember to watch before adding? * How does the direction of the rxn affect these things? * **^^EXAMPLE PROVIDED^^**

Answer 134

**ΔH_rxn** *is the **enthalpy change** for a reaction* **_TO CALCULATE:_** * ΔH_rxn usually calculated by **adding reactions** (and their associated enthalpy changes) **from a table** * You must select the reactions from the table that— when **added** together—will produce the **net** reaction for which you are calculating ∆H_RXN * To calculate ∆H_RXN you will **add** all of the values given for each of the reactions you use _*Paying careful attention to ​**SIGNS** and **STOICHIOMETRY***_ * If the reaction proceeds in the **SAME** direction as it would in the net reaction * use the value given **DIRECTLY** * If it proceeds in the **OPPOSITE** direction * **CHANGE THE SIGN** of the value given * You **MUST** multiply the number given in the table **by the coefficient** in the balanced net reaction* * For example, suppose one of the reactions given was the formation of liquid **water** from the elements **hydrogen** and **oxygen**: **½O₂ + H₂⇒H₂O** **∆H° f = -285 kJ/mol** * ...but in your **net** reaction water is a **reactant** * (**rather** than a product) * You would need to: 1. **CHANGE** the sign of ∆H° to be **positive**, and 2. **Combine it** with the enthalpy changes from **other** reactions used If your balanced net reaction contained **TWO** moles of water, you would need to **DOUBLE** the value given, and so forth

Question 135

2 L container of water and 4 L container of water Compare their heat capacities and specific heat capacities

Answer 135

Heat capacity of 4L is twice as much as other, b/c theres more water available to absorbSpecific heat capacities are the same in both

Question 136

As far as the MCAT is concerned, ___ is the only thing that changes K

Answer 136

temperature

Question 137

KMnO4What is oxidation state of Mn? Why?

Answer 137

+7

Question 138

For a reaction to occur, what 2 things have to happen with regards to **collisions**?

Answer 138

1) Reactants must collide with **enough energy** to **OVERCOME** E_a "hill" 2) Reactants must be in **correct SPATIAL orientation**

Question 139

# Define the **SECOND LAW** of Thermodynamics (has 2 parts!)

Answer 139

1. Heat cannot be changed **COMPLETELY** into work in a **cyclical** process 2. ∆S in an **isolated** system can **never** **decrease**

Question 140

Don't confuse standard state with?

Answer 140

STP values!

Question 141

∆G=∆H-T∆S (+) (+)What is ∆G?

Answer 141

∆H is unfavorable∆S is favorable∆G is dependent on Temp! Will be favorable (-) only if Temp is high enough

Question 142

Heat Exchange * What happens when heat **ENTERS** a system? * Does the temperature **ALWAYS** increase? * Is any increase in temperature always **EXACTLY** proportional to the heat **absorbed** by that system? **Hint**: Think of adding energy to a **sealed** **steel** **container** vs. adding energy to a **balloon** * remember that temperature is the average KE of the molecules, but an **increase** in temperature is **NOT** the only “**place**” where added energy can go

Answer 142

*PV work is the work necessary* ***to produce an increase in VOLUME*** * For example, when a sealed balloon is heated, the gases inside the balloon will **expand** and must do work on the rubber walls of the balloon and the air around it to accomplish this expansion * Because **some** of the heat energy added to the balloon was used for **pv work**, only the **REMAINING** portion of the heat will go toward increasing the average KE of the molecules (i.e., temperature) _So, when heat **enters** a system, if the system is **capable** of volume change, heat can go to **either:**_ * pv work * increased temperature (av. KE) * or **BOTH** * For this reason, the addition of a certain amount of heat will **NOT** **necessarily** be **EXACTLY** proportional to the resultant* * increase in temperature* _If the system is **NOT** capable of changing volume:_ * **NO** pv work can be done * ∴ **ALL** of the added heat will go toward an increase in temperature

Question 143

What is a **CALORIMETER**? * What do we assume about "**q**?"

Answer 143

**CALORIMETER:** *a device used to calculate ∆H* * assume **q = ∆H** * which is **true** at **~P**

Question 144

Acid-Base Equilibria You should think of **K_a** or **K_b** just as you do \_\_\_? * A large **K_a** (or a small **pK_a**) indicates **WHAT?** * A large **K_b** (or a small **pK_b**) indicates **WHAT?**

Answer 144

**You should think of K_a or K_b just as you do K_eq** A _**large Ka** (or a **small pKa**) indicates that at equilibrium:_ * more **products** \> **reactants** * For an acid dissociation, this would mean **a lot** of dissociation * (i.e., a lot of **H+ formed**) * And thus a **_very strong acid_** _Similarly, a **large Kb** (or a **small pKb**) indicates a **very strong base**_ * i.e., a lot of ^-**OH** **FORMED,** either from: 1. **Dissociation** of a **hydroxide base** * i.e., NaOH 2. ...or from **deprotonating** **water**

Question 145

Acid-Base Equilibria * Give the formula for: **IONIZATION OF WATER**

Answer 145

***H₂O + H₂O ⇔ H₃O⁺ + OH^-*** | (H₃O⁺ is the same as H⁺ )

Question 146

* Acid-Base Equilibria Ionization of Water, **H₂O + H₂O ⇔ H₃O⁺ + OH^-** * What is K_water (or just "K_w") at 25°C? * What is pK_water equal to? (HINT: \_\_+\_\_= #) Show how the equation for pK_w is **DERIVED** **FROM** K_w

Answer 146

**K_water = [H₃O⁺][OH^-] = 10^-14** ## Footnote (at 25° C) ***Remember: H₃O⁺ is the same as H⁺*** This caveat should make sense * because you learned earlier that **TEMPERATURE** is the **one** thing that **DOES** change K_eq * *(​This is why 25C **IS** included here)* **pK_water = pH + pOH = 14** _DERIVATION,_ *Starting with:* **K_w = [H₃O⁺][OH^-] = 10^-14** First, we take the **negative log** of all terms, yielding: **logKw = -log[H³O⁺] + -log][OH^-] = -log(10^-14)** The **middle two** terms come from the log rule that states: * logAB = logA + logB The **first term** can be **replaced** with **pKa** by definition The **second term** with **pH** by definition The **third term** with **pOH** by definition The **fourth term** by **14** * because 14 **IS** the –log of 10^-14! This leaves: **pK_w = pH + pOH = 14**

Question 147

* Acid-Base Equilibria Ionization of Water, **H₂O + H₂O ⇔ H₃O⁺ + OH^-** * pK_a + pK_b= ?

Answer 147

**14**

Question 148

Acid-Base Equilibria * Acid Dissociation * Give the **equation** that represents **Acid Dissociation** * K_a=? ​HINT: "HA"

Answer 148

**HA + H₂O ⇔ H₃O⁺ + A^-** ## Footnote (H₃O⁺ is the same as H⁺) * **K_a = [H⁺][A^-] / [HA]**

Question 149

Acid-Base Equilibria * Acid Dissociation, **HA + H₂O ⇔ H₃O⁺ + A^-** * ​Acid **H-X** dissociates **80%** in water *Would you expect its K_a to be **greater** than,* ***less** than, or **equal** to ONE?* HINT: **K_a= [H⁺][A^-] / [HA]**

Answer 149

Because the acid **almost fully dissociates:** * we know that the ratio of products over reactants would have to be **GREATER** than one _An acid is considered “**STRONG**” when:_ * **K_a \> 1,** or a * **pK_a \< 0** *...so **this** acid would **clearly** qualify as a **strong** acid*

Question 150

Acid-Base Equilibria * Acid Dissociation * With regards to **K_a** and **pK_a** values, what makes an acid "**STRONG**?"

Answer 150

_An acid is considered “**STRONG**” when:_ * **K_a \> 1** ​OR * **pK_a \< 0**

Question 151

Acid-Base Equilibria * Base Dissociation * Give the **formula** that represents a base dissociating in water * What is **K**_b equal to? * How do K_a and K_b **COMBINE** * to create K_w? *_HINT_: "HA" is to **ACID** Dissociation as **"A^-"** is to **BASE** Dissociation*

Answer 151

**_Base Dissociation:_** **A^-+H₂O ⇔ OH^- + HA** **K_b = [OH^-][HA] / [A^-]** **(K_acid ) x( K_base) = K_water = 10^-14** (at 25°C) * because ([H+][A-]/[HA])\*([OH-][HA]/[A-]) = [H+][OH-] = Kw

Question 152

Acid-Base Equilibria * Base Dissociation * **T/F?** An aqueous solution with a **pH of 8** is **BASIC,** and therefore by definition it does **NOT** contain **ANY** *unreacted* H⁺ ions

Answer 152

**FALSE** ## Footnote * An aqueous solution with a pH of 8 **IS** basic * but that does **NOT** mean that it does **not** contain **any** hydrogen ions In fact, the presence of hydrogen ions is easily **verified** * **​**by solving the formula pH = -log[H⁺] for [H⁺] * There are 1.0 x 10^-8 moles of hydrogen ions per liter of **this** solution _It is classified as "basic" because:_ * it has **fewer** **hydrogen** ions than are found in neutral water * and **more** **hydroxide** ions than are found in neutral water

Question 153

Acid-Base Equilibria * When you see **ACID / BASE:** ***THINK?***

Answer 153

_**Balance** between:_ **[OH^-] and [H⁺] ions!**

Question 154

Acid-Base Equilibria * Base Dissociation * Acid A has a K_b of 1.0 x 10^-9 * Acid B has a K_b of 1.0 x 10^{-10 ​}Which acid will create the **largest** **DECREASE** in pH when added in equimolar amounts to pure water? * aka, will Acid A or Acid B make the water **more** acidic?

Answer 154

**Acid B will give the largest drop in pH** **_THE SMALLER Kb REPRESENTS THE STRONGER ACID_** * The **largest** decrease in pH will be caused by addition of the **most** acidic of the two species You **could** simply recognize from the equation: **Kw = Ka\*Kb** * ...that K_b and K_a are **inversely** related * therefore**THE _SMALLER_ K_b REPRESENTS THE _STRONGER_ ACID** * because **K_a** and **acid strength** are **directly** related

Question 155

Acid-Base Equilibria **SUMMARY:** * _How do:_ 1. **Ionization** of Water 2. **Acid** Dissociation, and 3. **Base** Dissociation *...RELATE to one another?*

Answer 155

* Ionization of water is often called the “**autoionization** of water” * because it happens **automatically** in **ALL** water * So, when an acid or a base is added to water the **autoionization equilibrium** is **ALREADY** **ONGOING** in that solution— * a process we can describe with an equilibrium constant, K_w * If we are at 25°C, we **know** that: 1. **K_w** will be **10^-14** and 2. The concentrations of **[H⁺] ions** and **[OH] ions** will both be **10^-7**M _**After** adding an acid or a base we suddenly have **TWO** equilibriums present in the **same** solution:_ * 1) The **ionization** of water, and * 2) The **equilibrium** for the acid or the base we added * Just as we described the **ionization of water** with an equilibrium constant, **K_w**,* * ...We can **also** describe the dissociation of the acid or base we added with **K_a** or **K_b***

Question 156

Acid-Base Equilibria **SUMMARY:** _An important key many students can't visualize is this:_ * When we add an **acid** or **base** to **water**, the **EQUILIBRIUM** of that acid or base will directly impact *WHAT?* * Explain yo'self! HINT: Use **H₂O + H₂O ⇔ H₃O⁺ + OH^-**

Answer 156

* When we add an acid or base to water, the equilibrium of that acid or base **will directly impact the equilibrium for the ionization of water*** * according to Le Chatelier’s Principle Looking at the formula, **H₂O + H₂O ⇔ H₃O⁺ + OH^-** * We can see that adding an **acid** will shift the equilibrium to the **left** * This will **use up** hydroxide ions (**OH^-**) * **Each** hydroxide ion that reacts will also use up * **ONE** hydronium ion (**H₃O⁺**) *But remember that we just added **EXTRA** hydronium ions **in the form of the acid*** * The **net** result will be **more** **hydronium** ions relative to **hydroxide** ions * and therefore a **LOWER** **pH** (Remember that the [OH-] **equaled** the [H+] **before** we added the acid)​

Question 157

**NEGATIVE** ΔG=?

Answer 157

**SPONTANEOUS!** Free energy **IS** available to do work!

Question 158

**POSITIVE** ΔG=?

Answer 158

**NON-SPONTANEOUS!** Energy is **NOT** available to do work! :(

Question 159

**WATER** has a **VERY HIGH** heat capacity because...?

Answer 159

You should know that water has a very high heat capacity... **due to hydrogen bonding**

Question 160

* For an **exo**thermic **decomposition** reaction, which of the following properties is(are) known? * I. the sign of ∆S * II. the sign of ∆H * III. if K is \> or \< 1 * IV. the sign of ∆G * A. I only * B. I & II * C. I, II & III * D. I, II, III & IV

Answer 160

**D** * The word “decomposition” tells us that we are going from **one** species to **two or more** species, meaning entropy must be positive * The word “exothermic” tells us that the enthalpy must be negative * Finally, from ∆G = ∆H - T∆S we know that if we plug in these two values Gibbs free energy must be negative * Because Gibbs free energy is negative, we also know that K must be greater than one from the equation: ∆G = -RTlnK * Thus, we know all of the items listed and the correct answer is D