1.5 Kinetics

Question 1

What is the definition of enthalpy?

Answer 1

Enthalpy is the total heat content of a system at constant pressure.

Question 2

True or False: Enthalpy change can be measured directly.

Answer 2

False

Question 3

What is the formula for calculating the change in enthalpy (ΔH)?

Answer 3

ΔH = H(products) - H(reactants)

Question 4

What does a negative ΔH value indicate?

Answer 4

It indicates that the reaction is exothermic.

Question 5

What does a positive ΔH value indicate?

Answer 5

It indicates that the reaction is endothermic.

Question 6

Fill in the blank: The standard enthalpy change of formation (ΔHf°) is the enthalpy change when one mole of a compound is formed from its elements in their _____ states.

Answer 6

standard

Question 7

What is the standard enthalpy of combustion (ΔHc°)?

Answer 7

It is the enthalpy change when one mole of a substance is burned completely in oxygen under standard conditions.

Question 8

What is Hess’s Law?

Answer 8

Hess’s Law states that the total enthalpy change for a reaction is the same, regardless of the number of steps in the reaction.

Question 9

True or False: The enthalpy change of a reaction is independent of the pathway taken.

Answer 9

True

Question 10

What is the unit of enthalpy?

Answer 10

Kilojoules per mole (kJ/mol)

Question 11

What is a calorimeter used for?

Answer 11

A calorimeter is used to measure the heat absorbed or released during a chemical reaction.

Question 12

What is the specific heat capacity?

Answer 12

The specific heat capacity is the amount of heat required to raise the temperature of one gram of a substance by one degree Celsius.

Question 13

Fill in the blank: The enthalpy change for a reaction can be calculated using the equation q = _____ × m × ΔT.

Answer 13

C

Question 14

What does ‘q’ represent in the equation q = C × m × ΔT?

Answer 14

Heat energy absorbed or released.

Question 15

What is the significance of standard conditions in thermodynamics?

Answer 15

Standard conditions refer to a pressure of 1 atm and a temperature of 298 K (25 °C).

Question 16

What is the relationship between bond enthalpy and enthalpy change?

Answer 16

Enthalpy change can be calculated using the bond enthalpies of bonds broken and formed.

Question 17

True or False: Bond enthalpies are the same for all molecules.

Answer 17

False

Question 18

What is the enthalpy change of a reaction if the bonds broken require 800 kJ and the bonds formed release 600 kJ?

Answer 18

ΔH = 800 kJ - 600 kJ = 200 kJ (endothermic)

Question 19

What does the term ‘enthalpy of solution’ refer to?

Answer 19

It refers to the enthalpy change when one mole of a solute dissolves in a solvent.

Question 20

Fill in the blank: The enthalpy change of neutralization is the enthalpy change when an _____ and a base react to form one mole of water.

Answer 20

acid

Question 21

What is the typical value of ΔH for a strong acid-strong base neutralization?

Answer 21

Approximately -57 kJ/mol

Question 22

What is the difference between endothermic and exothermic reactions?

Answer 22

Endothermic reactions absorb heat, while exothermic reactions release heat.

Question 23

What is the heat of fusion?

Answer 23

The heat of fusion is the enthalpy change required to convert a solid into a liquid at its melting point.

Question 24

What is the heat of vaporization?

Answer 24

The heat of vaporization is the enthalpy change required to convert a liquid into a gas at its boiling point.

Question 25

True or False: The heat of vaporization is generally greater than the heat of fusion for a substance.

Answer 25

True

Question 26

What is the significance of the enthalpy of formation for a compound?

Answer 26

It provides a reference point for calculating the enthalpy changes of reactions involving that compound.

Question 27

Fill in the blank: The enthalpy change of a reaction can be influenced by _____ and pressure.

Answer 27

temperature

Question 28

What is the standard state of an element?

Answer 28

The standard state of an element is its most stable form at 1 atm and 298 K.

Question 29

What is the purpose of a thermochemical equation?

Answer 29

A thermochemical equation shows the enthalpy change along with the balanced chemical equation.

Question 30

True or False: The enthalpy change of a reaction is always the same regardless of the physical state of the reactants and products.

Answer 30

False

Question 31

What is the enthalpy change for the reaction of water formation from hydrogen and oxygen?

Answer 31

ΔHf° = -286 kJ/mol (for the formation of liquid water)

Question 32

Fill in the blank: The enthalpy change of a reaction can be calculated using the _____ method if the direct measurement is not feasible.

Answer 32

Hess's

Question 33

What is the relationship between temperature and enthalpy for an ideal gas?

Answer 33

For an ideal gas, enthalpy increases with temperature at constant pressure.

Question 34

What is the enthalpy change of sublimation?

Answer 34

The enthalpy change associated with the transition of a substance from solid to gas without passing through the liquid state.

Question 35

True or False: The enthalpy of reaction can be determined from bond enthalpies if all bonds are identical.

Answer 35

True

Question 36

Fill in the blank: The enthalpy change during a phase change is _____ at constant temperature.

Answer 36

constant

Question 37

What is the significance of the enthalpy of reaction?

Answer 37

It indicates whether a reaction is spontaneous and the energy changes involved.

Question 38

What does the term 'thermochemistry' refer to?

Answer 38

Thermochemistry is the study of the heat energy associated with chemical reactions.

Question 39

Fill in the blank: The enthalpy change for a reaction can also be influenced by the _____ of the reactants.

Answer 39

concentration

Question 40

What is the formula for calculating the enthalpy change using calorimetry?

Answer 40

ΔH = -q / n, where q is the heat absorbed and n is the number of moles.

Question 41

True or False: The enthalpy change is the same for both forward and reverse reactions.

Answer 41

False

Question 42

What is the enthalpy change for a reaction if 1000 J of heat is absorbed and 2 moles of product are formed?

Answer 42

ΔH = 1000 J / 2 mol = 500 J/mol