Energy and Chemical changes

Which of the following is an example of an endothermic process?

• Condensation of steam

• Burning of wood

• Melting of ice

• Freezing of water

What does the term 'enthalpy' (H) refer to?

• The speed of a reaction

• The color of a substance

• The total heat content of a system

• The amount of light released in a reaction

What is the sign of ΔH for an exothermic reaction?

• Positive

• Negative

• Zero

• Cannot be determined

Which statement is correct about standard enthalpy of formation (∆Hfo)?

• It is always positive

• It refers to forming 1 mole of a compound from its elements

• Elements have a ∆Hfo of 1 kJ/mol

• It only applies to gases

• 1

• 2

• 3

• 4

Which equation correctly represents a standard enthalpy of formation reaction?

• 2H₂(g) + O₂(g) → 2H₂O(l)

• 2Na(s) + Cl₂(g) →2 NaCl(s)

• CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(g)

A reaction has ΔH = +92 kJ/mol. Which statement is true?

• The reaction is exothermic and releases 92 kJ.

• The reaction absorbs 92 kJ of energy.

• The temperature of the surroundings will increase.

• The reaction occurs spontaneously.

Why is the combustion of methane exothermic?

• More energy is used to break bonds than is released.

• The reaction requires continuous heating.

• The bonds formed in products release more energy than the bonds broken in reactants.

• The products are less stable than the reactants.

The ∆H_f^o of O₂(g), H₂(g), and N₂(g) is zero because:

• They are gases

• They are noble gases

• They are elements in their standard states

• They are not reactive

Which of the following statements about bond energy and enthalpy of formation is correct?

• Both bond energy and enthalpy of formation always have negative values.

• Bond energy usually has a positive value, enthalpy of formation can be positive or negative.

• Both bond energy and enthalpy of formation always have positive values.

• Bond energy usually has a negative