Pass papers theory Flashcards
What type of motion does ATOMS have?
translational motion only
what type of motion does MOLECULES have?
translational
vibrational and
rotational motion
First law of thermodynamics can be given as…
- energy can neither be created nor destroyed
- the energy of an isolated system is constant.
- ΔE = q + w
the pH at the equivalence point of a weak acid- strong base titration increases
… as the Ka decreases
the advantage of using enthalpy rather than internal energy to describe energy changes
it provides us with a state function which allows us to focus on heat flow which is easier to measure than the work which accompanies a process.
Reason for using a calorimeter to measure heat changes in a chemical reaction is:
to account for all of the heat evolved or absorbed during the reaction
when does entropy increase?
- When a substance changes from a solid to a liquid or
- from a liquid to a gas or
- solid dissolves in a solvent or
- Raising the temperature of a system increases the kinetic energy of molecules or
- where the number of product molecules is greater than the number of reactant molecules or
- When a gas expands into a larger volume or into a vacuum.
the internal energy change for a process and the enthalpy change for the same process differ by an amount that is directly related to..
the work done on (or by) the system
ΔH = ΔU -PΔV
and PΔV = work
the thermodynamic standard states of any substance
25 degrees Celsius and 1 atm
Decrease in the entropy of the system, the entropy change of the surroundings will be:
larger than the entropy decrease of the system
Why unsaturated hydrocarbons are more reactive than saturated hydrocarbons?
the π component of the C-C double/triple bond is relatively weak.
second law of thermodynamics states
for any spontaneous reaction, the entropy of the universe increases
third law of thermodynamics states that…
the entropy of a pure, crystalline substance at absolute zero is zero.
when a molecule is heated gently what happens to its molecules?
there is an increase in the translational and rotational motion
when an atom is heated gently what happens to its molecules?
there is an increase in translational motion only.
For an EXOTHERMIC reaction, if the temperature of a reaction is DECREASED, the effect it will have on ΔG and the equilibrium constant is …
ΔG decreases and
K increases
as T and K are directly proportional whereas ΔG and T and inversely proportional
entropy is a measure of?
the randomness of a system
what equation relates ΔG and E?
ΔG = -nFE
carbon atoms that are bonded to a halide are Electrophilic or nucleophilic?
electrophilic
What is electrophilic substitution?
- Electrophilic substitution: An electrophile (something lacking electrons) attacks an electron-rich molecule
- Often in aromatic rings (like benzene) because they’re electron-rich and attract electrophiles.
- Adding Br to benzene.
what is nucleophilic substitution?
- A nucleophile (something with extra electrons) attacks an electron-poor spot on a molecule
- Common in alkyl halides (carbon with halogen) because the halogen makes the carbon electron-poor, which attracts nucleophiles.
- Replacing Cl in a compound with OH.
the most correct statement about Bronsted lowery acids and Lewis acids are
every Bronsted- Lowry acid is also a Lewis acid
Pure water…
is a poor conductor of electricity
conjugate acids of weak bases produce
more acidic solutions than conjugate acids of strong bases.
what quantities are the properties of a system?
- internal energy
- temperature
- enthalpy
- volume
- work is NOT part of the system
when a system is in equilibrium
the process is not spontaneous in either direction
true or false?
The extent of ionization of a weak electrolyte is increased by
adding to the solution a strong electrolyte that has an ion in
common with the weak electrolyte.
False
True or false?
For any buffer system, the buffer capacity depends on the
amount of acid and base from which the buffer is made
True.
Which of the salts are acidic?
(a) Ba(CH3COO)2,
(b) NH4Cl, (c) KNO3, (d) Al(ClO4)3.
b- NH4Cl and
d- Al(ClO4)3
An acid that have the highest equivalence point is (strong/weak)?
weak
Work done on the system by the surroundings leads to a (positive/negative) value?
positive value.
ΔE = q + w
how do you calculate the molar heat capacity given the specific heat capacity?
molar heat capacity = Cs x molar mass
with thermodynamics one can determine…
the temperature at which a reaction will be spontaneous
State functions
- entropy
- Enthalpy
- Gibbs free energy
- internal energy
- temperature
- pressure
path functions
- work
- heat
what process produces the greatest increase in entropy of a substance?
vaporizing a liquid
what equation relates temperature and the equilibrium constant?
ΔG = -RTlnK
when they are all at standard thermodynamic conditions.
When a real gas under pressure is allowed to expand suddenly (adiabatically)
which changes occur?.
- the temperature drops
- its entropy increases
- heat is converted into disorder
A large value of the standard reduction protentional indicate a ________ reaction.
spontaneous
How many Chiral carbons does b- glucose have?
5 chiral carbons
What product can undergo electrophilic substitution?
the benzene ring
Lewis Acid
- accepts an electron pair
- these are electrophiles
What statement is most consistent for an acid with a pH = 3?The acid is:
100 times as strong as an acid with a pH= 5
when dealing with specific heat how will it be affected by the highest final temperature?
the one with the lowest specific heat
What Increases for a spontaneous process …
the total entropy of the system and surroundings increase
a reaction come to equilibrium when it reaches?
its minimum Gibbs energy
True/ False?
a non spontaneous process cannot be caused to occur under any circumstances?
False
True/False
a Spontaneous reaction is one that does not require an external energy source to proceed
true
The highest entropy will have the ____ molar mass
the one with the highest Mm
if a process is exothermic: the entropy of the surroundings:
will sometimes increase and sometimes decrease depending on the process
Structure of Benzene
- undergoes electrophilic substitution
- exhibits resonance
- delocalized electrons make it very stable
- carbons are sp2 hybridized and therefore the ring structure is planar.
True/False
An indicator is chosen so that the pKa is more or less equal to the pH at the equivalence point?
True.
true/false
A buffer consists of either a weak acid and its salt or a weak base and its salt
true
Explain by means of equations what is meant by a competitive reaction using CH3CH2Br
- Competitive reactions occur when a substrate molecule can undergo different types of reactions with the same reagent. Eg substitution or elimination reactions
- CH3CH2Br + NaOH → CH3CH2OH + NaBr
CH3CH2Br + NaOH → CH2=CH2 + NaBr + H2O
Name two factors that influence the direction of such competitive reactions
- Temperature
- Structure of the substrate molecule
the major factor determining the increase in acidity of binary acids (HX, where X = F, Cl, Br, I_ going down a column of the period table is:
decreasing the H-X bond strength
to find the equilibrium constant given ka and kb we use the formula:
Kc = (ka x kb) ÷ kw
NB: Kw = 1.o x 10 ^ -14
Which of each of the following salts will be neutral: (a) Na(CH3COO)2,
(b) NH4Cl, (c) KNO3, (d) MgCl2?
KNO3 and MgCl2
When asked to calculate absorbance (A) what are the 2 equations you can use?
- Beer- Lamberts law A = ε x L x C
- transmittivity relationship : A = -log (T)
When calculating fuel Value we use:
mass (g) x Fuel value in KJ/g
I. in an open vessel at constant atmospheric pressure q is equal to?
II. in a closed vessel q is equal to?
ΔH = q for and open vessel and ΔE = q for a closed vessel
What is expected to happen to the V and w when the reaction shown below takes place in a thermally-insulated container outfitted with a movable piston at a constant atmospheric pressure of 1 atm?
2 C2H6(g) + 7 O2(g) → 4 CO2(g) + 6 H2O(g)
Volume will increase and work will be done BY the system
An ideal gas expands into a vacuum (external pressure = 0) without gaining or losing heat. For this expansion what happens to ΔG?
ΔG does not change as there is no work being done (in a vacuum) and no heat gained or lost.
Will the condensation of water vapor be an exothermic or endothermic reaction?
exothermic
name the endothermic reactions
- Ice melting
- water evaporating
- boiling
for an endothermic reaction when we decrease the temperature what happens to K and ΔG?
- K DECREASES and
ΔG increases
in which case will work done on the system be positive?
When ΔV < 0, because
w = -PΔV
A galvanic cell consists of one half-cell that contains g Ag(s) and Ag+(aq), and one half-cell that contains Cu(s) and Cu2+(aq). What species are produced at the electrodes under standard conditions?
Ag(s) is formed at the cathode, and Cu2+ (aq) is formed at the anode.
true/false
the hydroxide ion is a weaker nucleophile than water?
false
in an ester what takes the suffix -yl and what takes the suffix -oate?
- yl: comes from the alcohol part and -oate comes from the carboxylic acid part
Which one of the following salts, when dissolved in water, produces the solution with the lowest pH?
A. NaCl
B. KCl
C. MgCl2
D. AlCl3
E. LiCl
AlCl3
Which of the following combinations of chemicals could be used to make a buffer solution?
A. HCl / NaOH
B. HCl / NH3
C HCl / H3PO4
D NaOH / NH3
E. HCl / NaCl
HCl/NH3
Under what condition(s) is the enthalpy change of a process equal to the amount of heat transferred into or out of the system? ΔH = q
(i) temperature is constant
(ii) pressure is constant
(iii) volume is constant
pressure is constant
Which of the following is True? The internal energy of a system can be increased by:
(i) transferring heat from the surroundings to the system
(ii) transferring heat from the system to the surroundings
(iii) doing work on the system
- transferring heat from the surroundings to the system
- doing work on the system
What is a criterion for spontaneity that holds for any process?
ΔS(total) > 0
when ΔG = ΔG° what is happening with the equilibrium constant?
Q = 1
when the system performs work On the surroundings is w (positive/negative)?
negative
what actions change the measured cell potential?
- a change in the pH
- increasing/ decreasing the pressure at the cathode part
- increasing the [ion]
what does a large NEGATIVE value of the standard reduction potentials indicate?
a non-spontaneous reaction
An electrolytic cell is a cell in which:
a nonspontaneous reaction is forced to occur
What would make this statement TRUE?
Carboxylic acids are produced when tertiary alcohols are treated with a
strong reducing agent.
carboxylic acids are produced when PRIMARY alcohols are treated with a strong reducing agent such as LiAlH4
when asked for the temperature at which a reaction will be spontaneous/ nonspontaneous what equation do you use?
T = ΔH° ÷ ΔS°
For an endothermic reaction, decreasing temperature will have the following effects on K and ΔG
ΔG more positive (increases) and
-decreases 𝐾
What is buffer capacity?
is the amount of acid/base the buffer can neutralize before the pH begins to change to an appreciable degree.
what is meant by fuel value of a substance?
It is the amount of heat produced when 1 g of a substance is combusted.
when does H= q?
under constant pressure (such as in an open system exposed to atmospheric pressure), the heat (q) added to or released from the system equals the change in enthalpy ΔH.
the strength of an oxyacid depends on?
the electronegativity of the central atom
Which one of the binary compounds will have the highest acid strength? HF, HCl, HBr, HI or H2O
HI (the halogen with the least H-X bond)
HF is a weak acid
What equation do we use to calculate the ratio of an Base: an Acid
Handerson hasselbalch
pH = pKa + log [B]/ [A]
what does a buffer depend on?
large concentrations of a weak acid and a conjugate base
What hinders buffer capacity
the greater the amounts of conjugate acid-base pair the more resistant is the ratio of their concentrations and hence pH to change.
the greater the buffer capacity…
the greater the amount of the conjugate acid-base pair
what is the optimum pH of any buffer?
pH =pka
the highest buffering capacity has the (highest/lowest) concentration
highest
what are the units of Ɛ
dm3. mol-1. cm-1
The enthalpy change for the reaction: 3C2H2(g )→ C6H6(l) is negative. What can be concluded with regards to the enthalpy?
1 mol of C6H6 has LESS enthalpy that 3 mol of C2H2
a chemical reaction that is spontaneous will proceed…
without outside intervention
the first law of thermodynamic can be stated as:
ΔE = q + w
Which change is always positive when a spontaneous process occurs?
ΔS(universe)
what equation relates molar enthalpy, entropy and mols
ΔS (fusion) = (ΔH x n) ÷ ΔT
Fill in:
1. ΔG > 0
2. ΔG = 0
3. ΔG < 0
- non- spontaneous
- at equilibrium
- spontaneous
how is reactivity influenced in ringed alkanes?
Smaller rings have higher ring strain, making them more reactive.
Benzene behaves differently from a hydrocarbon which simply contains three
C=C bonds. From a thermodynamic point of view, the hydrocarbon would be
expected to react much more readily with:
A. H2
B. Cl2
C. Br2
D. HCl
all of them as they are all addition reactions and you can add them across the double bond
can a tertiary amine form hydrogen bonds?
no, as there are no hydrogens connected to an electronegative nitrogen.
what is the chemical equation when you add KOH to a buffer solution such as acetic acid with sodium acetate?
CH3COOH + KOH ⇌ CH3COO- + H20 + K+
the magnitude of Kw indicates that…
water autoionizes only to a very small extent
The hydride ion, H-, is a stronger base than the hydroxide ion, OH-. The product(s) of the reaction of hydride ion with water is/are:
OH- + H2
Which one of the following 0.1 M solutions has a pH of 7.0?
A. Na2S
B. KF
C. NaNO3
D. NH4Cl
E. NaF
NaNO3
what is an oxyacid? And how does the the strength increase?
an acid that has oxygen attached to a central atom. For oxyacids with the same central atom the acidity increases with the number of oxygen atoms attached to the central atom.
What is the strongest acid among the following?
A. HBrO
B. HBrO2
C. HBrO3
D. HBrO4
E. HBr
As for HBr, it is a strong acid but not an oxyacid, and in this context of comparing oxyacids, HBrO₄ is the stronger choice due to the increasing oxygen effect
What can make a buffer mixture?
- a weak acid and its weak conjugate base or
- a Strong acid/base with enough of a weak base/ acid
Under what condition(s) is the internal energy change( ΔU) of a process equal to the amount of heat transferred into or out of the system? ΔE = q
(a) temperature is constant
(b) pressure is constant
(c) volume is constant
constant volume only
When a system is at equilibrium is the reverse or forward reaction spontaneous?
none. the process is not spontaneous in either direction
With thermodynamics one CANNOT determine?
the speed of the reaction
what can thermodynamics predict about a reaction?
- the direction of a spontaneous reaction
- the extent of a reaction
- the value of the equilibrium constant
- the temperature at which a reaction will be spontaneous
does entropy (increase/decrease) going down the group of halogens?
DECREASES
What feature must a molecule or ion have to act as a Lewis base?
it must have an unshared pair of electrons which can be shared with another atom
if ΔG° for a reaction is less than zero then K will be…
K > 1
For which of the following is the standard Gibbs free energy of formation equal to zero?
(a) H2O(l)
(b) O(g)
(c) Cl2(g)
Cl2 (g)
in an electrolytic cell a (spontaneous/ nonspontaneous) reaction needs to occur?
a nonspontaneous reaction is forced to occur
Electrolyisis reactions are…
reactions in which work is done on the reaction system
How do you calculate the pH in a dilution
- Find the no. of moles in each acid before the dilution (multiply by 2 if its a polyprotic acid)
- Add all the moles of the acid to get the total moles of the H+ that it contributed
- find the concentration of the H+ after the dilution
- Find the pH
What will happen if a small amount of HCL is added to a 0.1M solution of HF ( a weak acid)
the % ionization of HF (weak acid) will decrease
Which technique would be least suitable to separate the following:
A. Brewed coffee from it’s coffee grounds – filtration.
B. Chloroform (bp. 61 oC) from ether (bp. 35 oC) – distillation.
C. Separation of K+
and Ag+
ions – spectrophotometry.
D. The colour pigments of a leaf – chromatography.
E. Water from wet lettuce – centrifugation.
c- you cannot separate ions using spectrophotometry as it is used to measure the light absorbed by chemicals
what statements are correct regarding indicators?
- the are usually weak acids
- The pH at which an indicator changes colour depends on the pKa
- the point at which an indicator changes colour in a titration is termed the end point
- Bromothymol blue with a pKa of 7.1 is a suitable indicator for a strong acid - base titration
specific heat capacity is…
the quantity of heat needed to change the temperature of 1.00g of a substance by 1.00K
potential engery is measured in?
Joules
Electrochemical cell (voltaic/ Galvanic)
- converts chemical energy into electrical energy
- spontaneous rxn
- Anode is negative (oxidation)
- cathode is positive (reduction)
- electrons move from the anode to the cathode in the external circuit
- electrons supplied by the species getting oxidized
Electrolytic cell
- coverts electrical energy to chemical energy
- non spontaneous rxn (energy has to be supplied)
- Anode is POSITIVE ( oxidation)
- cathode is NEGATIVE ( reduction)
- external batteries supplies the electrons
- enter through the cathode and exit through the anode
according to the third law of thermodynamics, at 0 K there is zero entropy. this is because?
The atoms are ordered as there is no KINETIC energy at 0 K
- temperature always refers to kinetic energy
In a voltaic cell electrons always flow from…
the Anode to the Cathode
What would happen if a small amount of HCL is added to a 0.1M HF?
the % ionization of HF will decrease
what would happen is you add NaOH to a small amount of HF?
the %ionization of HF increases
if the pH decreased by 2. this means the concentration…
H+ increased by a factor of 100
formula: [H+] NEW / [H+] OLD
** use antilog for this.
precipitation is used to separate?
ions from each other
What energy does not change in a chemical reaction?
nuclear energy
How to calculate the heat absorbed/ released when given enthalpy? (H)
q = H x no. of moles ( H > 0 exothermic rxn)
q = -H x no. of moles ( H < 0 endothermic rxn)
the purpose of the salt bridge?
to maintain electrical neutrality in the half cells via migration of the ions
which of the following salts will give BASIC solutions when placed in water?
CH3COOK and Na2S
buffers…
- resists changes to pH upon the addition of small amounts of a strong acid/ strong base
- the way a buffer operates can be explained in terms of le chateliers principle
- should contain similar concentrations of a weak acid/ base and its conjugate base/ acid
if one mole of an acid neutralizes two moles of a base, then:
one mole of acid supplies two moles of hydrogen ions to the base
Δ H
- negative when exothermic
- positive when endothermic
- Δ H = qp
- when measured at 1 atm the enthaply change is read as Δ H°
internal energy
- is the sum of the energies of all atoms or molecules in a system
- extensive property
- increases with an increase in temp and mass
- is dependent on mass
- is not = 0 at 0 K due to the contribution of the nuclear and electronic energies
- during a chemical reaction, nuclear energy does not change
the internal energy of a system is always increased by?
Adding heat to the system
relationship between ka and percent ionization is?
directly proportional
* the weaker the ka the weaker the % ionized
at the equivalence point in an acid/base titration it is always correct to say?
Neither the acid nor the base is in excess.
Stronger attraction to the stationary phase
Longer retention time
Stronger attraction to the mobile phase
shorter retention time
When given the bond energies and asked to calculate the change in enthalpy what formula do we use?
ΔH = bonds broken - bonds formed
when an exothermic reaction takes place that is spontaneous despite a negative ΔS system is because?
ΔS surroundings increases and therefore ΔS universe is positive
Calorimeters measure heats of reaction in:
- Styrofoam cup where pressure is constant (coffee keeps pressures from rising)
- bomb cell calorimeters where volume is constant
True or false
Melting or vaporizing a substance at its melting and boiling point respectively is an isothermal process?
True
true/false
the total amount of energy obtained by a system equals the total amount of energy accumulated by its surroundings
false
True/ False
Alkanes are the simplest class of organic molecules because they contain no
functional groups.
true
True/ false
Structural isomers that belong to the same family display the same chemical
and structural properties.
False
an appropriate description of spontaneity is?
whether a reaction can do useful work at a certain temperature
the work done by the system during expansion is ______ and the heat ____ by the system is positive.
negative, gained
does the formation of rust from iron reacting with oxygen lead to an increase or decrease in entropy?
decrease in entropy
if a system undergoes a reversible isothermal process without the transfer of heat, the temperature at which this process takes place is called?
absolute zero
a refrigerator is a reverse heat engine which takes place from a ___ temperature vessel, the discharged it to a ____ temperature vessel and ____ an inward flow of energy.
low
high
receives
True/False
the standard reduction potential E (red) is proportional to the stoichiometric coefficient
False, it has no effect
What makes carbon such a unique element?
to a greater extent than any other element, carbon can bond to itself to form straight chains, branched chains and rings
True/ False
Enantiomers contains sp2 hybridized carbon atom with four different groups attached to it
FALSE
sp2 hybridization is for geometric isomers
Homologous series
a series of compounds belonging to the same functional group with different lengths of the carbon chains
An alkene opens to give you what hybridization?
sp3
LiAlH4:
This is a strong reducing agent, used to reduce aldehydes and ketones to alcohols. It’s not suitable for oxidation reactions.
PCC (Pyridinium Chlorochromate):
This is a mild oxidizing agent that can oxidize primary alcohols to aldehydes without further oxidation to carboxylic acids. This is the reagent most suitable for an oxidation reaction
OsO4:
This is a strong oxidizing agent that can cleave alkenes to form diols. It’s not suitable for this reaction
K2Cr2O7/H+
This is a strong oxidizing agent that can oxidize primary alcohols to carboxylic acids. It would over-oxidize the alcohol in this case.
KMnO4
This is also a strong oxidizing agent that can oxidize primary alcohols to carboxylic acids. It would also over-oxidize the alcohol.
WHat reaction would an aromatic hydrocarbon like benzene easily undergo?
Friedel crafts acylation
strong and weak nuclear forces
- strong nuclear forces hold the nucleus together
- weak nuclear forces are responsible for alpha and beta decay and play essential roles in splitting the nucleus of an atom
what is the relationship between enthalpy and internal energy?
ΔH = ΔE + PΔV
what is the relationship between the exponent of the concentration of the [OH-] and [H3O+] to its pOH/ pH respectively
its the same e.g. [H+] = 1x 10^-4.5 M , thus the pH= 4.5
for a conjugate acid/base pair…
the pKa + pKb = 14
is the carbon in organometals nucleophilic or electrophilic?
nucleophilic
a buffer that has a pH < 7 can be prepared by?
mixing approximately equal amounts of a weak acid and a salt of its conjugate base
according to the second law of thermodynamics
G system decreases in a spontaneous change at constant temperature and
pressure.
What is a surfactant?
compounds that lower the surface tension between two liquids
what is a zwitterionic surfactant?
they have both cationic and anionic centers attached to the same molecule
Micelle
- an aggregate of surfactant molecules dispersed in a liquid colloid
- its formation is essential for the transport of complicated lipids within the human body
Amphiprotic/ amphoteric
substances that can act as an acid or a base
polyprotic
a substance that can donate more than 1 proton
Which one of the following is NOT an amphoteric species in water?
A. H2CO3
B. HPO42─
C. HS─
D. H2O
E. HSO4─
H2CO3
electrostatic potential energy properties
- is measured in Joules.
- As an electron gets closer to the nucleus of an atom its PEel decreases.
- can have both positive and negative values
- PEel = q1q2 (where q1 and q2 are the charged particles and r is the 4r distance between them, is the permittivity of the medium).
- it is a scalar quantity
What are the conditions for when work is being done by the system on the surrounding?
- when there is an increase in the number of gas molecules.
- The formation of a gas from a solid results in an increase in the number of gas molecules, leading to work being done by the system on the surroundings
According to the second law of thermodynamics, for a spontaneous change,
what is always INCORRECT?
ΔS (total) < 0
Which nucleophiles requires the presence of an acid catalyst
in order to undergo an addition reaction with an aldehyde?
- water
- ethanol
the empirical formula of an addition polymer is…
the same as that of the monomer from which it is formed
benzene is immiscible in water because of:
weak solute-solvent interactions
the substance with the highest BP has the highest…
dipole moment
a typical emulsifying agent has?
a hydrophobic group and a hydrophilic group at opposite ends of the molecule
