MCAT CHEM CH. 6

Question 1

What is the zeroth law of thermodynamics?

Answer 1

Thermal system attempt to achieve thermal equilibrium with their surroundings

Question 2

What is the first law of thermodynamics?

Answer 2

The total energy of the universe is constant; energy cannot be created or destroyed

Question 3

What are the three distinct designations to describe energy flow?

Answer 3

1. The system
2. The surroundings
3. The universe

Question 4

What is the thermodynamics universe?

Answer 4

The system and the surroundings taken together

Question 5

What is enthalpy?

Answer 5

Measure of the heat energy that is released or absorbed when the bonds are broken and formed during a reaction

Question 6

When is delta H greater than zero?

Answer 6

When energy must be put into a bond in order to break it

Question 7

When is delta H less than zero?

Answer 7

When a bond is formed, energy is released

Question 8

What must happen in a chemical reaction to the reactants?

Answer 8

Energy must be put in into the reactants to break their bonds

Question 9

What happens while products form based on enthalpy?

Answer 9

Energy is released

Question 10

How is the enthalpy of a reaction given?

Answer 10

Difference between the enthalpy of the products and the reactants

Question 11

What is enthalpy change?

Answer 11

Heat of reaction

Question 12

What is exothermic? How is the enthalpy change?

Answer 12

Energy is released, less than zero

Question 13

What is endothermic?

Answer 13

Energy is absorbed, greater than zero

Question 14

What is the units for molecular weight?

Answer 14

g/mol

Question 15

What is the constants for standard conditions?

Answer 15

Temperature is 298 K (25 degrees) and pressure is 1 atm

Question 16

What are the conditions of the substance in standard conditions?

Answer 16

All solids and liquids are assumed to be pule

Question 17

What are the conditions of the solutions in standard conditions?

Answer 17

Considered to be at 1 M concentrations

Question 18

What is standard temperature and pressure?

Answer 18

0 degrees celsius

Question 19

What is standard conditions temperature?

Answer 19

25 degree celsius

Question 20

What is standard heat of formation?

Answer 20

Amount of energy required to make one mole of a compound from its constituent elements in their natural state

Question 21

What is the standard state enthalpy forms of elements?

Answer 21

Zero

Question 22

What is the standard state enthalpy forms for diatomic elements?

Answer 22

zero

Question 23

Why is the standard state enthalpy form of O not zero?

Answer 23

Because it takes energy to break the double bond

Question 24

What is the standard heat of formation prefix?

Answer 24

delta H degree sign, subscript f (go to page 126 to see it)

Question 25

What does it mean when standard heat of formation prefix is positive?

Answer 25

Input of heat is required to make that compound from its constituent elements

Question 26

What does it mean when standard heat of formation prefix is negative?

Answer 26

Making the compound from its elements gives off energy

Question 27

What is Hess’ law?

Answer 27

If a reaction occurs in several steps, the sum of the energies absorbed or released will be the same as that for the overall reaction

Question 28

What are the two important rules for Hess’ law?

Answer 28

1. If a reaction is reversed, the sign of delta H is reversed too
2. If an equation is multiple, delta H must be multiplied too

Question 29

Energy is needed to….

Answer 29

break a bond

Question 30

Energy is released to….

Answer 30

make a bond

Question 31

If a question provides a list of bond enthalpies, how can we determined delta H reaction? (Based on summation of average bond enthalpies)

Answer 31

delta H reaction = E (BDE bonds broken ) - E (BDE bonds formed)

Question 32

What is the second law of thermodynamics?

Answer 32

All processes tend to run in a direction that leads to maximum disorder

Question 33

What is used to measure disorder or randomness?

Answer 33

Entropy

Question 34

What is the symbol of entropy?

Answer 34

S

Question 35

What is the change in entropy’s equation?

Answer 35

delta S = S products - S reactants

Question 36

What is the third law of thermodynamics?

Answer 36

Defines absolute zero to be a state of zero-entropy

Question 37

How is thermal energy at absolute zero?

Answer 37

Thermal energy is absent

Question 38

What is the Gibbs free energy?

Answer 38

Energy that’s valable to do useful for from a chemical reaction

Question 39

What are the two tendencies for a spontaneous reaction?

Answer 39

Decrease enthalpy (release heat) and increase entropy (more disorder)

Question 40

What are the two tendencies for a non spontaneous reaction?

Answer 40

Increase in enthalpy, decrease in entropy (products have more energy and less disorder than the reactants)

Question 41

What if the Gibbs free energy is negative?

Answer 41

Spontaneous in forward direction

Question 42

What if the Gibbs free energy is equal to zero?

Answer 42

At equilibrium

Question 43

What if the Gibbs free energy is positive?

Answer 43

Nonspontaneous in the forward reaction

Question 44

What is the equation for the Gibbs free energy?

Answer 44

Delta G = delta H - T delta S

Question 45

What if delta S is positive and delta H is positive?

Answer 45

Spontaneous at high temperatures, non spontaneous at low temperatures

Question 46

What if delta S is negative and delta H is negative?

Answer 46

Nonspontaneous at high temperatures, spontaneous at low temperatures

Question 47

How are each symbol reported based on values? delta H and delta S

Answer 47

delta H = kJ, delta S in J

Question 48

What is Ea in the reaction energy diagrams?

Answer 48

The extra energy the reactants required to overcome the activation barrier and determines the kinetics of the reaction