Chemistry Exam 2

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Strong acids/ bases

Fully dissociates into ions in aqueous solution

What do weak acids/ bases look like when they dissolve?

Only partially dissolve into ions in solution

What is water’s charge?

None, it’s neutral 

Autodissociation of H₂O

2H₂O(l) ←—→ H₃O⁺(aq)+OH^-(aq)

What is neutralization in an acid-base reaction?

Acid + Base —→ Salt + Water

What are some special cases where the acid-base reactions create gas evolution reactions with either CO₂(g) or SO₂(g)?

CO₃^2-, HCO₃^-, SO₃^-, and HSO₃^-

Define titrations

Determining amount of chemical in an impure substance by slowly adding an aqueous solution of known concentration until chemicals have just fully reacted 

Analyte

Unknown concentration being analyzed

Titrant

Known concentration being added via buret

Equivalence point

When moles analyte = mole titrant only if 1;1 molecular ratio; otherwise proportionally equal

Indicator

Chemical added to analyte that changes color when equivalence point is reached

Endpoint

When titration stopped (color change observed). Ideally same as equivalence point

Electrical Conductivity

Ability of substance to transport e^- through it

What makes something have electrical conductivity?

Metals or ions

Conductivity of NaCl(s)

None

Conductivity of H₂O(l)

Almost none

Conductivity of tap water

Conductive, due to other ions though not H₂O

Strong electrolytes

Dissociate completely into ions 

What does it mean if there is lots of ions in something?

It has high conductivity

Weak electrolytes

Only partially dissociate into ions

Nonelectrolytes

Dissolve as neutral molecules (no conductivity) 

What are some factors of strong electrolytes?

Soluble salts, strong acids, and strong bases

What are some strong factors of weak electrolytes?

Partially soluble/ insoluble, weak acids, and weak bases

What are some factors of nonelectrolytes?

Water soluble covalent compounds

What do redox reactions transfer?

e^- from one species to another 

What is an oxidation reaction?

Charge increased/ lost e^-

What is a reduction reaction?

Charge decreased/ gain e^-

What are the four rules of assigning oxidation numbers 

1. Elements in natural form

2. Ions (ox = charge [on element]) 

3. Hydrogen usually +1 (depends) 

4. Oxygen usually -2

What are the types of redox reactions?

Combination, decomposition, displacement, and combustion

What are the four properties of gases?

1. Gases assume shape and volume of their container 

2. Gases can be compressed

3. Gas densities are very low but depend significantly on temperature and pressure 

4. Gases form solutions with other gases in any proportion 

Pascal (pa) =

1 N/m²

Millimeter of mercury (mmHg) = torr =

height of column of mercury at sea level = 760 mmHg

What is pressure?

Force exerted over an area

Boyles law example

Lungs

Boyles law equation 

P1V1 = P2V2 

Gay-Lussac’s law equation and what is it related to?

Pressure and temperature directly related (P1 / T 1 = P2 / T2)

Charles law directly related to and equation

Volume and temperature directly related (V1 / T1 = V2 / T2) 

Avogrados law directly related to and equation

Volume and moles directly related (V1 / n1 = V2 / n2)

Important things to remember about the combined gas law 

Remove any variables held constant and temperature must be in units of Kelvin 

What is the combined gas equation?

P1 V1 / n1 T1 = P2 V2 / n2 T2

What is the ideal gas equation?

Pv = nRT

What does R (in ideal gas equation) equal to?

0.08206 (L atm/ mol K) = 8.314 (J / mol K) 

What is an important thing to keep in mind about molar mass?

Should NEVER be less than 1

What is Dalton’s law of partial pressure?

When multiple gases are in a container together, each gas behaves as if it occupies the container along and the total pressure is a sum of all components partial pressures

What is the equation for total pressure?

Ptot = Sum of all pressures 

What are mole fractions used for?

Relative amounts of components in a gas mix to be specified

What is the sum of all mole fractions?

1

What is dimensionless? 

Mole fractions 

Mole fraction equation

Xi = (ni / ntot)

How are gas molecules separated?

By large distance, and each molecule’s volume is negligible

What exhibits perfectly elastic collisions?

Gas molecules as they bump into one another. Pressure results from bumping the sides of the container

Do gas molecules have attractive or repulsive forces between one another?

Nope

What does the temperature of a gas relate to?

The average kinetic energies of gas molecules in that sample

What is the average speed of a particle equation?

U_rms = √ (3RT / molar mass) —all under the square root!

Define diffusion 

Dispersing of gas in space due to differences in concentration

Define effusion

Diffusion through a small opening/ pinhole

What is Graham’s law?

(Rate A / Rate B) = √ (molar mass B / molar mass A)

What does Graham’s law apply to?

Both diffusion and effusion  

Do real gases always obey ideal gas laws?

Nope

How do actual gases react to gases having negligible volume?

At high pressures, molecules are close together and their individual volumes become significant

It’s assumed gases don’t interact with one another because molecules are far apart. What do actual gases do? 

At low temperatures, molecules are moving slower and interact more 

What is Van der Waal’s equation?

(P_measured + [an² / v²]) * (V_calculated - nb) = nRT.

What does “a” and “b” mean in Van der Waal’s equation?

a is the strength of attractive forces

b is the size of gas molecules

List (on a paper) The activity series 

Li

Ca

Na

Mg

Al

Ni

H₂

Au 

Define volume correction

Occupied space for gas is less than container —→ molecules take up space

Define pressure correction

Real pressure of a gas is smaller than expected due to molecular attractions

Define thermochemistry 

Study of heat transfers involved in physical process and chemical reactions 

Define energy

Capability to do work or transfer heat

Define potential energy

“Stored energy” —→ in chemistry, potential energy is stored in bonds

Define kinetic energy 

Energy of movement

What gets converted to kinetic energy

Potential energy

When will a reaction continue?

Reaching an energy minimum 

Define thermal energy

Type of kinetic energy caused by motions of atoms and molecules

Define temperature

A quantitative(number) measure of thermal energy

What is hot/cold considered? 

A qualitative measure of thermal energy 

What is the energy equation?

KE = (1/2)MV²

Define heat

Transfer of thermal energy due to temperature differences

Define work (in chemistry) 

All other types of energy transfers 

How do you find the change in energy?

△E = q + w

When is work positive?

When work is done on a system

When is work negative? 

When work is done by a system 

When heat goes in and work on system, what is the △E?

Always positive

Heat in, work by a system, what is the △E?

Either positive or negative

Heat out, work on system. What is the △E?

Either positive or negative

Heat out, work by system. What is the △E?

Always negative

What is a fun fact about energy of the universe? 

It is constant

What is joule equal to?

Energy when 1 Newton of force moves an object 1 meter

Define Calore (cal)

Energy needed to raise 1g H₂O and change it by 1^oC

What is joule equal to? 

(Kg m² / s²)

What does one calorie equal to?

4.184 J

What is Calorie (Cal)

Kcal, nutritional calorie

What does Cal equal to? 

1000 cal

Define heat capacity (C)

Heat transferred when 1 gram of a substance changes temperature by 1^oC

Define specific heat capacity

Heat transferred when 1 gram of a substance changes temperature by 1^oC

What is the heat capacity equation?

C = (q / △T) 

What is the specific heat capacity equation?

c = (q / m△T)

Define calorimetry

Technique used to measure heat changes of physical or chemical processes

What is the calorimetry equation? 

q = mC△T

What is calorimeter used for?

Devised to use calorimetric data

Define exothermic reactions

A process/ reaction that releases heat