Thermodynamics

Question 1

the laws of thermodynamics underlie any even in which ______ is transformed

Answer 1

energy

Question 2

the Zeroth Law

Answer 2

if two systems are both in thermal equilibrium with a third system, then the two initial systems are in thermal equilibrium with one another

Question 3

if systems are in thermal equilibrium, what does this imply about their temperatures?

Answer 3

their temperatures must be the same

Question 4

the First Law

Answer 4

the total energy of the universe is constant, energy may be transformed from one form to another, but it cannot be created or destroyed

Question 5

an isolated system has a constant ______

Answer 5

amount of matter and ENERGY: no transformation of the energy is possible

Question 6

how can a system increase its overall energy?

Answer 6

if work is put into its system

Question 7

what happens when energy flows into a system from the surroundings?

Answer 7

the energy of the system increases (+) and the energy of the surroundings decrease

Question 8

what happens when energy flows out of a system into the surroundings?

Answer 8

the energy of the system decreases (-) and the energy of the surroundings increase

Question 9

enthalpy, H

Answer 9

the measure of the heat energy that is released or absorbed when bonds are broken and formed during a reaction that’s run at constant pressure

Question 10

when a bond is formed, energy is:

Answer 10

released, enthalpy change is negative

Question 11

when a bond is broken, energy is:

Answer 11

put into the bond, enthalpy change is positive

Question 12

heat of reaction

Answer 12

enthalpy change, delta H

Question 13

when is enthalpy change negative, exergonic?

Answer 13

when the products of a chemical reaction have stronger bonds than the reactants, so that more energy is released in the making of product bonds than was put in to break chemical bonds

Question 14

how do you calculate enthalpy change?

Answer 14

enthalpy of products - enthalpy of reactants

Question 15

exothermic

Answer 15

energy is released overall from the system, enthalpy change is negative

Question 16

endothermic

Answer 16

energy is absorbed into the system, enthalpy change is positive

Question 17

standard conditions

Answer 17

298K (25 degrees Celsius), pressure is 1 atm, all solids and liquids are assumed to be pure, solutions are at a concentration of 1 M

Question 18

standard heat of formation

Answer 18

the amount of energy required to make one mole of a compound from its constituent elements in their natural or standard state

Question 19

what does it mean if standard heat of formation is a positive value?

Answer 19

an input of heat is required to make the compound from its constituent elements

Question 20

what does it mean if standard heat of formation is a negative value?

Answer 20

making the compound from its elements gives off energy

Question 21

Hess’s law

Answer 21

if a reaction occurs in several steps, then the sum of the energies absorbed or given off in all the steps will be the same as that for the overall reaction

Question 22

what does it mean that enthalpy is a state function?

Answer 22

the enthalpy change is independent of the pathway of reaction

Question 23

what happens to the value of enthalpy change if reaction is reversed?

Answer 23

the sign of enthalpy change is reversed too

Question 24

what happens to the value of enthalpy change if an equation is multiplied by a coefficient?

Answer 24

the enthalpy change must be multiplied by that same value

Question 25

enthalpies can be viewed as the energy stored in the chemical bonds of a compound that denotes how much energy is required to:

Answer 25

break the bond homolytically

Question 26

how do you calculate the enthalpy change of reaction?

Answer 26

sum of BDE of bonds broken - sum of BDE of bonds formed

Question 27

second law of thermodynamics

Answer 27

the disorder of the universe increases in a spontaneous process

Question 28

entropy

Answer 28

disorder or randomness, S

Question 29

what is the sign of entropy change if randomness increases and order decreases in a reaction?

Answer 29

positive

Question 30

what is the sign of entropy change if randomness decreases and order increases in a reaction?

Answer 30

negative

Question 31

what is the value of enthalpy change in a reverse reaction?

Answer 31

the same magnitude as that of the forward reaction but with opposite signs

Question 32

can reactions in which entropy decreases occur?

Answer 32

yes, but it would require either an input in energy or else it must gain energy from making more stable bonds

Question 33

The Third Law

Answer 33

absolute zero is a state of zero-entropy

Question 34

Gibbs free energy (delta G)

Answer 34

the energy that's available (free) to do work from a chemical reaction

Question 35

what is the spontaneity of a reaction determined by?

Answer 35

changes in enthalpy and in entropy, included by G

Question 36

what is the formula for Gibbs free energy

Answer 36

G=H-TS

Question 37

what does it mean if Gibbs free energy is negative?

Answer 37

it is spontaneous in the forward direction

Question 38

what does it mean if Gibbs free energy is zero

Answer 38

the reaction is at equilibrium

Question 39

what does it mean if Gibbs free energy is positive

Answer 39

it is nonspontaneous in the forward direction

Question 40

if delta G is positive for a reaction, then what is the value of delta G for the reverse reaction?

Answer 40

it would be the same magnitude but opposite sign, so that the reverse reaction is spontaneous

Question 41

what does entropy depend on?

Answer 41

temperature; increased temperature=entropy has greater significance

Question 42

the universe tends towards...

Answer 42

increasing disorder (positive S) and stable bonds (negative H), a favourable condition of S and H will result in spontaneous processes

Question 43

what is the delta G of the overall reaction?

Answer 43

the difference between the energy of the products and the energy of the reactants

Question 44

the activation energy determines:

Answer 44

the kinetics of the reaction: it is the extra energy the reactants are required to overcome

Question 45

thermodynamics predicts:

Answer 45

the spontaneity and the equilibrium of reaction, not the rates (kinetics)

Question 46

microscopic reversibility

Answer 46

the reverse reaction has the same magnitude for all thermodynamic values but of the opposite sign, and the same reaction pathway but in reverse (mirror images)

Question 47

what is different for forward and reverse reactions?

Answer 47

activation energy