Exam 3

What is the formula mass for carbon dioxide, CO₂?

• 12 amu

• 28 amu

• 44 amu

• 56 amu

Based on the balanced equation below, how many moles of H₂O can form from the reaction of 5 moles of CH₄?

CH₄(g) + 2O₂(g) --> CO₂(g) + 2H₂O(g)

• 2.5 moles

• 5 moles

• 10 moles

• 15 moles

How many moles are present in 44.0 grams sulfur?

• 0.727 moles

• 1,410 moles

• 32.06 moles

• 1.38 moles

What is the limiting reagent in this reaction?

• Br₂

• Al

• AlBr₃

• H₂O

Based on the balanced equation below, how many moles of SF₆ can form from the combination of 11.0 moles of S with 20.0 moles of F₂?

S + 3F₂ --> SF₆

• 11.0 moles SF₆

• 20.0 moles SF₆

• 6.67 moles SF₆

• 31.0 moles SF₆

A chemist carries out this reaction in the laboratory, using 4.31 grams of zinc and an excess of sulfur:

Zn + S --> ZnS

From the balanced equation, she calculates that she should obtain 6.41 grams of zinc sulfide. However, she only isolates 5.30 g of product. What is her percent yield for this reaction?

• 1.8%

• 67.2%

• 120.9%

• 82.7%

Changes in energy can take place in what two forms?

• heat and work

• potential and kinetic

• thermofission and nucleosis

• heat and temperature

Energy is often stored in the form of chemical bonds. This is a type of

• kinetic energy

• potential energy

• heat energy

A candy bar contains 515.0 kilocalories of stored chemical energy. What is this energy in kilojoules?

• 0.123 kJ

• 123.1 kJ

• 8.12 X 10^-3 kJ

• 2,155 kJ

When a solid melts, it absorbs heat from its surroundings. This is a(n) process.

• endothermic

• exothermic

• thermoneutral

• exergetic