Honors Unit 6 Thermochemistry

What does the Law of Conservation of Energy state?

• Energy can be destroyed
• Energy transforms into matter
• Energy can be created
• Energy cannot be created or destroyed
• Energy only flows in one direction

Answer explanation

The law states energy is conserved — it cannot be created or destroyed.

In thermochemistry, what is the 'system'?

• Everything in the universe
• Air around the lab
• Chemicals being studied
• Thermometer reading
• Only the surroundings

Answer explanation

The system is the specific part of the universe under study, like reacting chemicals.

Which direction does heat flow in an exothermic process?

• From surroundings to system
• From system to surroundings
• No flow occurs
• Into the core
• Only upward

Answer explanation

Exothermic = heat exits the system to surroundings.

Classify the following: Ice melting.

• Exothermic
• Endothermic
• Neutral
• Combustion
• Decomposition

Answer explanation

Melting absorbs energy → endothermic.

Which of the following is an exothermic process?

• Boiling water
• Melting ice
• Candle burning
• Evaporation
• Baking bread

Answer explanation

Candle burning releases heat to surroundings — exothermic.

Choose all processes that are endothermic.

• Freezing
• Melting
• Boiling
• Condensation
• Sublimation

Answer explanation

Melting, boiling, and sublimation all require energy input → endothermic.

What is the energy change for the surroundings if a system gains energy?

• Surroundings gain energy
• No change
• Surroundings also gain energy
• Surroundings lose energy
• Energy is destroyed

Answer explanation

If the system gains energy, the surroundings lose it — total conserved.

Fill in the blank: In an exothermic reaction, energy flows from the ______ to the ______.

Answer explanation

Exothermic reactions release energy from system to surroundings.

What is the sign of ΔH for an endothermic reaction?

• Negative
• Positive
• Zero
• Undefined
• Depends on mass

Answer explanation

ΔH is positive when energy is absorbed (endothermic).

Which of the following real-life processes is endothermic?

• Condensation of steam
• Lighting a match
• Baking bread
• Freezing water
• Combustion of gasoline

Answer explanation

Baking requires heat input — endothermic.