unit 7 study guide

Question 1

thermodynamics laws

Answer 1

0) If two things are the same temperature as a third, they are also the same temp.
1) Energy is Conserved, ΔEuniverse = 0
2) Energy spreads out, ΔSuniverse > 0

3) A perfect crystal at Absolute Zero
has zero entropy, S = 0.

Question 2

enthalpy

Answer 2

state function

H = E + PV

Question 3

entropy

Answer 3

entropy (S) – the degree of disorder.
The “order” of a system is just as important
S > 0 means more disorder.

Question 4

gibbs free energy

Answer 4

To simplify various calculations and comparisons, and to make full use of the 2nd Law of Thermodynamics, chemists define another term, Gibbs Free Energy:

	    G = H – TS

Where H = enthalpy, T = temperature, and S = entropy. G is a state function because H, T, and S are state functions.

Question 5

what reactions are spontaneous without help and what causes rxn to be spontaneous

Answer 5

Exothermic reactions usually take place spontaneously (without help)

High energy -low energy
Order -disorder

These natural processes together drive reactions to continue spontaneously

Question 6

whats inequality equation for exothermic rxn

Answer 6

ΔH<0

Question 7

inequality equation for edothermic rxn

Answer 7

ΔH>0

Question 8

hess’ law

Answer 8

Hrxn° = nHf°,products – mHf°,reactants

where n and m are the stoichiometric coefficients.

Question 9

breaking bonds is what type of reacrion

Answer 9

endothermic

Question 10

work

Answer 10

w = F × d

Question 11

pv work

Answer 11

most common
p/FA
Gases can do work through expansion or compression against a constant external pressure. Work done by gases is also sometimes called pressure-volume or PV work for reasons that will hopefully become more clear in this section! Let’s consider gas contained in a piston.

Pressure–volume work. Pressure–volume work (or PV work) occurs when the volume V of a system changes. PV work is often measured in units of litre-atmospheres where 1L.

Question 12

specific heat

Answer 12

q=mcat (mc delta t)
Where q is the heat gained by the system, c is the specific heat of the substance, m is the mass, and ΔT is the change in temperature (in °C or K). Every substance has a different specific heat capacity, which is the amount of heat required to raise one gram of it 1 °C.

Question 13

kinetics factors

Answer 13

The speed of a reaction depends on:

1) Temperature
2) Concentration
3) Surface area (for solids)
4) Catalysts / inhibitors

Question 14

temp in kinetics

Answer 14

) Temperature: The hotter a reaction is, the more reactants have enough energy to react. (Hotter = faster reaction)

Question 15

concentration in kinetics

Answer 15

The more concentrated a solution is, the more often reactants collide. (More concentrated = faster reaction)

Question 16

surface area in kinetics

Answer 16

(for solids): Finer powders allow more reactants to collide. (More surface area = faster reaction)

Question 17

catalysts/inhibitors in kinetics of rxn

Answer 17

Catalysts can speed a reaction by aligning reactants or by changing the reaction mechanism.

Question 18

kinetic molecular theory

Answer 18

A theory of the thermodynamic behavior of matter, especially the relationships among pressure, volume, and temperature in gases, based on the dependence of temperature on the kinetic energy of the rapidly moving particles of a substance.

The kinetic theory describes a gas as a large number of submicroscopic particles (atoms or molecules), all of which are in constant rapid motion that has randomness arising from their many collisions with each other and with the walls of the container.

Question 19

rate law

Answer 19

The rate law of a given reaction is a concise mathematical formula that describes the instantaneous rate of that reaction under various conditions.

The rate law of a reaction can only be determined experimentally!

Question 20

rate law gen form

Answer 20

The general form of a rate law is:

	Rate = k [A]^x [B]^y [C]^z

k is the rate constant
(depends on temperature and state of reagents)

A, B, and C are reactants, (catalysts, or inhibitors)

x, y, and z describe how the rate depends on the concentration of A, B, and C

Question 21

order of reaction

Answer 21

In chemical kinetics, the order of reaction with respect to a given substance (such as reactant, catalyst or product) is defined as the index, or exponent, to which its concentration term in the rate equation is raised. … Reaction orders can be determined only by experiment.

Question 22

rate constant

Answer 22

The general form of a rate law is:

	Rate = k [A]x [B]y [C]z

k is the rate constant

Question 23

equilibrium

Answer 23

Equilibrium is the state at which forward and reverse rxns occur at the same rate, so the concentration of all species remains constant.

Given enough time, all reactions will eventually reach equilibrium. However, many reactions never reach equilibrium (e.g. rusting metal, living systems, etc.).

Question 24

equilibrium constant

Answer 24

Keq > 1 products are favored
Keq&raquo_space; 1 almost entirely products
Keq < 1 reactants are favored
Keq &laquo_space;1 almost entirely reactants

Question 25

Le Châtelier’s Principle

Answer 25

Any reaction at equilibrium that is disturbed by a change in concentration, pressure or temperature will shift its equilibrium position to counteract the change.

Question 26

heterogenous equilibrium

Answer 26

The concentrations of reactants and products are typically expressed as “activities” for equilibriums. The activity of a chemical is the ratio of its concentration or pressure and its standard value.

1) The equilibrium constant is unitless
2) Heterogenous chemicals (e.g. solids in an aqueous rxn) have an activity of 1
3) The rxn solvent has an activity of 1 if other species have low concentrations

Question 27

what kind of reactions are spontaneous only at low temperatures

Answer 27

deltaG= deltaH<0 and delta S<0

Question 28

what kind of reactions are spontaneous only at high temperatures

Answer 28

deltaG= deltaH>0 and deltaS>0

Question 29

if you add a catalyst to a reaction, where will the equilibrium go

Answer 29

products

Question 30

if you increase the temperature of a reaction, where will the equilibrium go?

Answer 30

products

Question 31

if you decrease the volume of the reaction vessel, where will the equilibrium go?

Answer 31

the reactants