8.1 Energy in Chemical Bonds

ΔH value in an endothermic reaction is a positive number.

• True
• False

What type of reaction is shown in the graph?

• endothermic reaction

• exothermic reaction

C+ O₂ --> CO₂ + 60kJ

what is the ΔH for the reaction?

• +60

• -60

• there is no way to know

Which symbol represents Enthalpy change?

• ΔH

• ΔT

• ΔG

• ΔS

usually in chemistry the pan here is...

• the system

• the universe

• the surroundings

• system + surroundings

Is this equation endo- or exo-thermic?

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

• endothermic

• exothermic

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

What symbol represents Enthalpy change?

• ΔH

• ΔT

• ΔG

• ΔS

The reaction represented goes essentially to completion. The reaction takes place in a rigid, insulated vessel that is initially at 600 K

Which of the following statements about the bonds in the reactants and products is most accurate?

• The sum of the bond enthalpies of the bonds in the reactant is greater than the sum of the bond enthalpies of the bonds in the products.

• The sum of the bond enthalpies of the bonds in the reactant is less than the sum of the bond enthalpies of the bonds in the products.

• The length of the bond between carbon and oxygen in CH₃OH is shorter than the length of the bond between carbon and oxygen in CO.

• All of the bonds in the reactant and products are polar.