AP Chem 6.7 Enthalpy and Thermochemistry Worksheet

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

• The reaction in a cold pack

• The reaction in a hot pack

• Burning wood

• Freezing water

What does bond enthalpy (energy) refer to?

• Whether a bond in pi or sigma

• The speed at which a bond forms

• The enthalpy change when a covalent bond is broken or formed

• The number of bonds in a molecule

Which statement is true about the energy involved in breaking and forming bonds?

• Both breaking and forming bonds involves the input of energy (endothermic).

• Breaking a bond requires energy, while forming a bond releases energy

• Both breaking and forming bonds release energy

• Breaking a bond releases energy, while forming a bond requires energy

Which process is exothermic in this diagram?

• neither is exothermic

• the breaking of the H-H and O=O bonds

• the formation of the

  O-H bonds in H₂O

Which formula is used to calculate the enthalpy change (ΔHrxn) of a reaction using bond energies?

• ΔHrxn = Σ(bonds broken) – Σ(bonds formed)

• ΔHrxn = Σ(bonds formed) – Σ(bonds broken)

• ΔHrxn = Σ(products) – Σ(reactants)

• ΔHrxn = Σ(reactants) + Σ(products)

If you are given the bond energies for all bonds in a reaction, what is the first step in calculating ΔHrxn?

• Add up all the reactant bond energies

• Add up all the product bond energies

• Subtract product bond energies from reactant bond energies

• Draw the Lewis structures for all molecules

Which of the following is the correct balanced equation for the reaction: CH₄(g) + Cl₂ → CCl₄(g) + HCl(g)?

• CH₄(g) + Cl₂ → CCl₄(g) + HCl(g)

• CH₄(g) + 4Cl₂ → CCl₄(g) + 4HCl(g)

• CH₄(g) + 2Cl₂ → CCl₄(g) + 2HCl(g)

• 2CH₄(g) + 4Cl₂ → 2CCl₄(g) + 4HCl(g)

If you are given the bond energies for all bonds in the reactants and products, what is the correct formula to calculate ΔH for a reaction?

• ΔH = Total bond energies of products - Total bond energies of reactants

• ΔH = Total bond energies of reactants - Total bond energies of products

• ΔH = Total mass of products - Total mass of reactants

• ΔH = Total number of atoms in products - Total number of atoms in reactants

HCl reacts with Zn giving off heat. This reaction must be (a)   .

• endothermic
• exothermic

Answer explanation

Exo - Means exits

Endo - Means enters.