8.4 Calculating Phase Changes & Identifying Entropy Changes

Multiple Choice

What instrument would you use to detect an endothermic or exothermic reaction?

• pH probe

• ruler

• temperature probe

• digital balance

Multiple Choice

How much heat is required to vaporize 50 grams of water? (Hv for water 540 cal/g)

• 20000 cal
• 27000 cal
• 30000 cal
• 25000 cal

Multiple Choice

The heat of fusion for sodium chloride (NaCl) is 30.2 kj/mole and the melting point is 801 degrees Celsius. How much heat is needed to melt 5.2 moles of NaCl?

• 120.5 kj
• 157.04 kj

• 75.3 kj
• 200.1 kj

Multiple Choice

The heat of fusion for sodium chloride (NaCl) is 30.2 kj/mole and the melting point is 801 degrees Celsius. How much heat is needed to melt 625 grams of NaCl?

• The heat needed to melt 625 grams of NaCl is 326 kJ.

• The heat needed to melt 625 grams of NaCl is 100.8 kJ.
• The heat needed to melt 625 grams of NaCl is 600.2 kJ.
• The heat needed to melt 625 grams of NaCl is 250.5 kJ.

Multiple Choice

Entropy is a measure of

• accuracy

• precision

• the disorder of a system

• the attraction of a nucleus for an electron

Multiple Choice

Entropy always increases when

• enthalpy decreases.
• temperature decreases.
• temperature increases.
• volume increases.

Multiple Choice

Entropy of a system increases when a reaction increases the number of particles.

• True

• False

Multiple Choice

What phase of matter has the most entropy?

• solid

• liquid

• gas

Multiple Choice

Which sample has the lowest entropy?

• 1 mole of KNO₃(l)

• 1 mole of KNO₃(s)

• 1 mole of H₂O(l)

• 1 mole of H₂O(g)

Multiple Choice

Which phase change represents a decrease in entropy?

• solid to liquid

• gas to liquid

• liquid to gas

• solid to gas