Energy Changes in Chemical Reactions

Is this equation endo- or exo-thermic?

PCl₃ (s) + Cl₂ (g) --> PCl₅ (s) + energy

• endothermic

• exothermic

Is this equation endo- or exo-thermic?

2KNO₃ (s) + energy --> 2KNO₂ (s) + O₂

• endothermic

• exothermic

Is this reaction endo- or exo-thermic?

NH₄NO₂ + energy --> N₂ (g) + 2H₂O (g)

• endothermic

• exothermic

When new chemical bonds form, energy ____________.

• is taken into the system.

• is released from the system.

• stays the same in the system.

When the solids Ba(OH)₂ and NH₄SCN are mixed, a solution is produced and the temperature drops. Which statement about the energetics of this reaction is correct?

• The reaction is endothermic and ΔH is negative

• The reaction is endothermic and ΔH is positive

• The reaction is exothermic and ΔH is negative

• The reaction is exothermic and ΔH is positive

The following equation shows the formation of magnesium oxide from magnesium metal. Which statement is correct for this reaction?

2Mg(s) + O₂(g) → 2MgO(s) ΔH = -1204 kJ

• 1204 kJ of energy are released for every mole of magnesium reacted

• 602 kJ of energy are absorbed for every mole of magnesium oxide formed

• 602 kJ of energy are released for every mole of oxygen reacted

• 1204 kJ of energy are released for every two moles of magnesium oxide formed

Does breaking bonds require energy, release energy, or not involve energy at all?

• requires energy to break

• releases energy when broken

• No energy involved

Based upon the graph above, what type of reaction is this?

• Endothermic

• Exothermic

In the graph above, what does D represent?

• activation energy

• products

• reactants

• enthalpy change

Which of the following represents an exothermic reaction?

• 
•