Energetics Ai

Question 1

What is the definition of enthalpy?

Answer 1

Enthalpy is the total heat content of a system, represented by the symbol H.

Question 2

True or False: Enthalpy change is the heat content change at constant pressure.

Answer 2

True

Question 3

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

Answer 3

ΔH = H(products) - H(reactants)

Question 4

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

Answer 4

standard

Question 5

What is the unit of enthalpy change?

Answer 5

Kilojoules per mole (kJ/mol)

Question 6

What does a negative ΔH value indicate?

Answer 6

It indicates that the reaction is exothermic.

Question 7

What does a positive ΔH value indicate?

Answer 7

It indicates that the reaction is endothermic.

Question 8

What is the standard enthalpy change of combustion?

Answer 8

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

Question 9

Calculate the enthalpy change if 100 kJ of heat is absorbed.

Answer 9

ΔH = +100 kJ

Question 10

What is Hess’s Law?

Answer 10

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

Question 11

True or False: The enthalpy change of a reaction can be determined by the sum of the enthalpy changes for individual steps.

Answer 11

True

Question 12

What is the formula for calculating the enthalpy change using bond enthalpies?

Answer 12

ΔH = Σ(bond enthalpies of bonds broken) - Σ(bond enthalpies of bonds formed)

Question 13

Fill in the blank: The enthalpy of reaction can also be expressed as the heat absorbed or released at constant _____ and volume.

Answer 13

pressure

Question 14

What is the significance of the standard state?

Answer 14

The standard state is the most stable form of a substance at 1 atm pressure and a specified temperature, usually 298 K.

Question 15

What is the standard enthalpy change of neutralization?

Answer 15

The enthalpy change when one mole of water is formed from the reaction of an acid and a base.

Question 16

Calculate the enthalpy change for a reaction if the energy required to break bonds is 500 kJ and the energy released from forming bonds is 300 kJ.

Answer 16

ΔH = 500 kJ - 300 kJ = +200 kJ

Question 17

What is meant by ‘specific heat capacity’?

Answer 17

Specific heat capacity is the amount of heat required to raise the temperature of 1 gram of a substance by 1 degree Celsius.

Question 18

What is the formula for calculating heat energy (q)?

Answer 18

q = mcΔT

Question 19

True or False: The heat energy absorbed by a substance can be calculated using its mass, specific heat capacity, and temperature change.

Answer 19

True

Question 20

What does ‘ΔT’ represent in the heat energy equation?

Answer 20

ΔT represents the change in temperature.

Question 21

What is the standard enthalpy of formation for elements in their standard state?

Answer 21

Zero (0 kJ/mol)

Question 22

Fill in the blank: The enthalpy of vaporization is the heat required to convert a unit mass of a substance from _____ to vapor.

Answer 22

liquid

Question 23

What is the enthalpy change for a reaction if the total energy of products is 1200 kJ and the total energy of reactants is 1000 kJ?

Answer 23

ΔH = 1200 kJ - 1000 kJ = +200 kJ

Question 24

What type of reaction is characterized by the absorption of heat?

Answer 24

Endothermic reaction

Question 25

What type of reaction is characterized by the release of heat?

Answer 25

Exothermic reaction

Question 26

What is the standard enthalpy change of reaction for the decomposition of water?

Answer 26

The standard enthalpy change of reaction for the decomposition of water is positive.

Question 27

Calculate the heat change when 50 g of water is heated from 20°C to 100°C, given specific heat capacity of water is 4.18 J/g°C.

Answer 27

q = 50 g * 4.18 J/g°C * (100°C - 20°C) = 16720 J

Question 28

What is the enthalpy change when 1 mole of methane is burned?

Answer 28

It is the standard enthalpy of combustion of methane.

Question 29

Fill in the blank: The heat of fusion is the heat required to convert a unit mass of a substance from _____ to solid.

Answer 29

liquid

Question 30

What is the relationship between bond strength and enthalpy change in a reaction?

Answer 30

Stronger bonds require more energy to break, resulting in larger enthalpy changes.

Question 31

What is the term for the heat absorbed or released during a chemical reaction?

Answer 31

Thermochemical change

Question 32

True or False: The calorimeter is an instrument used to measure the heat of reactions.

Answer 32

True

Question 33

What is the principle behind a bomb calorimeter?

Answer 33

It measures the heat of combustion of a sample under constant volume.

Question 34

What does the term 'latent heat' refer to?

Answer 34

Latent heat refers to the heat required for a substance to change its state without changing its temperature.

Question 35

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

Answer 35

temperature

Question 36

What is the effect of increasing temperature on the enthalpy change of an endothermic reaction?

Answer 36

It increases the enthalpy change.

Question 37

Calculate the enthalpy change for a reaction with a ΔH of -150 kJ.

Answer 37

The reaction is exothermic with an enthalpy change of -150 kJ.