Midterm 2

Question 1

Energy

Answer 1

capacity to do work or transfer heat

Question 2

work

Answer 2

energy that causes a mass to be moved by applying a force

work=-pΔV

Question 3

Heat

Answer 3

q.. energy that causes the temperature to go up

Question 4

Matter possesses energy in the form of

Answer 4

1) kinetic energy
2) thermal energy (heat)
3) potential energy

Question 5

kinetic energy

Answer 5

energy of motion of an object

Question 6

thermal energy

Answer 6

kinetic energy of molecules .. more motion, hotter the object

Question 7

potential energy

Answer 7

position of object.. stored energy due to position or composition

Question 8

difference between thermal and kinetic energy

Answer 8

kinetic moves in one direction.. thermal is individual molecules (which are all moving in different directions)

Question 9

calories

Answer 9

defined such that 1cal=4.184J

1 calorie = 1000 cal = 1 kcal

Question 10

open system

Answer 10

can exchange matter and energy with the surroundings

Question 11

closed system

Answer 11

can only exchange energy with the surroundings (ex heat)

Question 12

isolated system

Answer 12

neither matter nor energy are exchanged with the surroundings

Question 13

First law of thermodynamics

Answer 13

the total energy of the universe is conserved.. any energy lost by the system is gained by the surroundings and vice versa.

ΔU=q+w

q+=heat added, q-=heat released
w+=work done on, w-=work done by system

Question 14

U

Answer 14

internal energy - total energy possessed by a system

ΔU=q+w

ΔU=Uf-Ui or ΔU=Uproducts-Ureactants

Question 15

state function

Answer 15

A property of a system that is determined by the state or condition of the system and not by how it got to that state. It’s value is fixed when P,V,T,G&S are specified

(non-state = g, w)

Question 16

enthalpy

Answer 16

ΔH

-the heat change at constant pressure is the change of enthalpy of the system

Question 17

thermochemical equation

Answer 17

1) depends on amounts of reactants and products
2) ΔH forward = -ΔH reverse
3) ΔH depends on the physical state of reactants and products

balanced chemical reaction and the value of ΔH.. **Provides relationship between amounts of chemicals and the enthalpy change

Question 18

heat capacity

Answer 18

amount of heat required to raise the temperature of an object by 1K (or 1°C)

-depends on size of object bonding, complexity, physical state

Question 19

specific heat capacity

Answer 19

It is the amount of heat required to change the temp of a gm of a substance by 1°C.

Cs… can be determined experimentally

q=CsXmass(g)XΔT

Question 20

calorimetry

Answer 20

measure of heat flow

Question 21

constant pressure calorimetry

Answer 21

measures ΔHrxn

heat flows between reaction and solution at constant pressure

at constant P, qrxn =ΔHrxn

Question 22

constant volume calorimetry

Answer 22

measures ΔUrxn

heat from chemical reaction absorbed by water and all components of calorimeter

at constant V, qrxn = ΔUrxn

Question 23

Hess’s Law

Answer 23

The enthalpy change of an overall process is the sum of the enthalpy changes of its individual steps - combines the individual reactions so their sum gives the desired reaction
-can be used for both chemical and physical changes

-magnitude of ΔH depends on T, P and physical state of prod and reacts.

Question 24

standard enthalpy change

Answer 24

ΔH°rxn. (°means under standard conditions)..

the enthalpy change for a reaction with reactants and products in their stable forms at 1atm and 298K.

Question 25

standard enthalpy of formation ≈

Answer 25

ΔH°f the enthalpy change that accompanies the formation of one mole of a substance from its elements, with all substances in their standard states for pure elements in their most stable form at standard conditions.. ΔH°f=0

Question 26

Steps to take using ΔH°f to calc ΔH°rxn

Answer 26

- decompose reactants into elements - recombine elements into products ΔH°rxn =ΣnΔH°f (products) - ΣnΔH°f (reactants)

Question 27

fuel value

Answer 27

energy released when one gram of substance is combusted

Question 28

foods and fuel value

Answer 28

carbs ≈ proteins < fats fats easily stored. excess carbs not readily stored, and protein used to build

Question 29

Fuels and fuel value

Answer 29

natural gas>gasoline>coal (E/mass)

Question 30

Spontaneity

Answer 30

physical and chemical change tends to favour one direction over the other.. spontaneous process occurs without ongoing outside intervention

Question 31

nonspontaneous process

Answer 31

can occur only when the surrounding does work on the system or transfers energy to or from it

Question 32

Reversible process

Answer 32

the change occurs in such a way that both the system and the surroundings can be restored to their original states by exactly reversing the change in a reversible change, the max possible work is done

Question 33

Irreversible process

Answer 33

the system and the surroundings cannot both be returned to original state Spontaneous reactions are always irreversible

Question 34

Entropy

Answer 34

(S) a function that measures randomness in a system

Question 35

entropy changes

Answer 35

ΔS JK^-1 depends on heat and temperature phase changes are examples of isothermal processes ΔS = qrev / T = ΔH(phase change)/T

Question 36

second law of thermodynamics

Answer 36

In any spontaneous process, the total entropy of the universe increases ΔSuniv>0 (for a spontaneous process)

Question 37

Entropy increases for these processes

Answer 37

``` solid->liquid->gas #moles or elements of products higher than number of reactants ```

Question 38

Third law of thermodynamics

Answer 38

The entropy of a pure crystaline substance at 0K is zero - sets a baseline for further experiments because we know zero at 0K. - Absolute value of entropy, S, can be determined by measuring how much entropy rises as a crystal is warmed from 0K.

Question 39

Entropy changes in chemical reactions

Answer 39

1) heating increases molecular motion and entropy | 2) phase changes are isothermal, entropy changes sharply

Question 40

Standard molar entropy

Answer 40

the entropy value for a mole of a substance in its standard state - gases>liquid>solid - increases with molar mass - increases with number of atoms

Question 41

Change in entropy

Answer 41

ΔS°sys= ΣnS°(products)- ΣnS° (reactants) ΔSsurroundings= -qsys/T at constant P for isothermal process.

Question 42

Gibbs Free Energy

Answer 42

Thermodynamic state function that combines enthalpy and entropy, G=H-TS the process is spontaneous and ΔG must be negative.. ΔG determined the direction of spontaneous change In any spontaneous process at constant T and P, free energy decreases, ie ΔG is negative ΔGsys=ΔHsys-TΔSsys or

Question 43

Gibbs determining positive or negative

Answer 43

ΔG>0 the reaction is not spontaneous in the forward direction. work must be done to make it occur ΔG=0 the reaction mixture is at equilibrium

Question 44

Standard free energy of formation

Answer 44

Defined for formation of 1 mole of substance from its composed elements in their standard states. ``` temperature = 298 K pressure = 1 atm (gases) pure liquid or solid unit molarity (solutions) ``` elements in most stable form ΔG°f=0

Question 45

When ΔH & ΔS have same sign..

Answer 45

the sign of ΔG depends on how big they are

Question 46

Free energy and the equilibrium constant

Answer 46

Most chem reactions do not occur under standard conditions, and need to obtain ΔG from ΔG° ΔG=ΔG°+RTlnQ R=gas constant Q=reaction quotient Q depends on actual, nonstandard conditions and is useful in predicting the direction of a reaction

Question 47

Q predicting direction of a reaction

Answer 47

QK reaction is spontaneous from right to left Q=K equilibrium The direction of sponteneity can be changed by altering the concentrations of reactants and prods, which changes Q, and the value of ΔG

Question 48

Relationship between ΔG and K

Answer 48

At equilibrium ΔG=0 and Q=K

Question 49

Equilibrium:concentrations

Answer 49

concentrations of reactants and products become constant over time at equilibrium, concentration of reactants and products are not equal but they are unchanging.. reaction continues even @ equilibrium

Question 50

Equilibrium constant

Answer 50

Kc = equilibrium constant when concentrations are in M

Question 51

Evaluating Kc

Answer 51

insert equilibrium concentrations into kc expression

Question 52

equilibrium constants and pressure

Answer 52

Kp - same as kc but with P instead of concentrations

Question 53

Magnitude of equilibrium constants

Answer 53

the value of Kc (or Kp) indicates how far the reaction will proceed towards products 10^-3 - 10^3 = significant concentration of both products and reactants

Question 54

direction of net reaction

Answer 54

depends on the relative values of Qc & Kc When Q>K, there are more products than reactants. To decrease the amount of products, the reaction will shift to the left and produce more reactants. When Q

Question 55

Le Chateliers principle

Answer 55

If an equilibrium is distrubed by changing concentrations, T, or P, the equilibrium will shift to try to counteract the change [A] = will shift to use up or replace added/taken away concentrations V & total pressure = partial pressures change and Qp & Kp are not at equilibrium. ^ in total pressure = reaction shifts toward fewer moles of particles

Question 56

Free energy and equilibrium constant

Answer 56

direction of spontaneity can be changed by altering the concentrations of reactants & products, which changes Q and therefore changes the value of ΔG

Question 57

Temp effect of equilibrium

Answer 57

values changes with temp.. ``` endothermic = heat is a reactant exothermic = heat is a product ``` System adjusts to counteract this heat change

Question 58

Q

Answer 58

Reaction quotient: the value that is obtained when concentrations of reactants and products are inserted into the equilibrium expression. If the concentrations are at equilibrium: Q=K, if not Q does not = K