Understanding Enthalpy and Thermochemistry

What does the first law of thermodynamics state?

• Energy is always increasing in a system.

• Energy is conserved and cannot be created or destroyed.

• Energy can be created and destroyed.

• Energy is only transferred within a system.

What is the enthalpy change when a system absorbs heat?

• Negative, indicating heat loss.

• Zero, indicating no change.

• Positive, indicating heat gain.

• Variable, depending on the system.

Which type of reaction is typically associated with a positive enthalpy change?

• Combination reactions

• Neutralization reactions

• Combustion reactions

• Decomposition reactions

What is the enthalpy change for a system that releases heat?

• Zero, indicating no change.

• Negative, indicating heat loss.

• Variable, depending on the surroundings.

• Positive, indicating heat gain.

Which process involves a positive enthalpy change due to breaking intermolecular forces?

• Deposition

• Melting

• Condensation

• Freezing

What is the enthalpy change when a liquid turns into a gas?

• Negative, due to energy release.

• Positive, due to energy absorption.

• Zero, as no energy is involved.

• Variable, depending on the pressure.

Which process is the reverse of sublimation?

• Boiling

• Melting

• Deposition

• Condensation

How can the enthalpy of deposition be determined?

• By measuring the temperature change.

• By taking the opposite sign of sublimation.

• By adding the enthalpies of fusion and vaporization.

• By subtracting the enthalpy of fusion from vaporization.

What is the enthalpy change for a process that combines melting and boiling?

• Zero, as no energy is involved.

• Positive, as energy is absorbed.

• Negative, as energy is released.

• Variable, depending on the substance.

Which two enthalpy values are typically listed in chemistry reference manuals?

• Condensation and sublimation

• Fusion and condensation

• Vaporization and deposition

• Fusion and vaporization