Chemistry Practice Problems II

Chemistry Practice Problems II
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Question 1

Perform each conversion between energy units.

  • 356 cal to kJ
  • 2.31 x 106 kJ to kcal
  • 4.49 x 103 kJ to kWh
  • 6.15 x 104 J to Cal

Question 2

An unknown mass of each of the following substances, initially at 23.0°C, absorbs 1930 J of heat. The final temperature is recorded as indicated. Find the mass of each substance.

  • Pyrex glass (Tf = 55.8°C)
  • Sand (Tf = 62.0°C)
  • Ethanol (Tf = 44.2°C)
  • Water (Tf = 32.1°C)

Question 3

A 32.8 g iron rod, initially at 22.2°C, is submerged into an unknown mass of water at 63.1°C, in an insulated container. The final temperature of the mixture upon reaching thermal equilibrium is 58.4°C. What is the mass of the water?

Question 4

Mothballs are composed primarily of the hydrocarbon naphthalene (C10H8). When 1.025 of naphthalene (is burned in a bomb calorimeter, the temperature rises from 24.25 °C to 32.33 °C. Find ΔErxn for the combustion of naphthalene. The heat capacity of the calorimeter, determined in separate experiment, is 5.11 kJ/°C.

Question 5

Consider the following generic reaction: A + 2B à C + 3D, DH = 118 kJ. Determine the value of DH for each of the following reactions:

  • 3A + 6B –> 3C + 9D
  • C + 3D –> A + 2B
  • 1/2C + 3/2D –> 1/2A + B

Question 6

  • Write an equation for the formation of BF3(g) from it elements in its standard states.
  • Find DHf° for BF3(g)

Question 7

  • Write an equation for the formation of CaCO3(s) from its elements in its standard states. Write any reference to carbon as C(s).
  • Find DHf° for CaCO3(s)

Question 8

  • Write an equation for the formation of C2H4(g) from its elements in its standard states. Write any reference to carbon as C(s).
  • Find DHf° for C2H4(g).

Question 9

  • Write an equation for the formation of C2H5OH(l) from its elements in its standard states. Write any reference to carbon as C(s).
  • Find DHf° for C2H5OH(l).

Question 10

  • Write a balanced equation for the combustion of methanol, Note that the products of this combustion are gaseous carbon dioxide and liquid water.
  • ΔH°rxn
  • Determine the mass of carbon dioxide emitted per kJ of heat produced.
  • Calculate the same quantity for octane C8H18. DHrxn° = -5074.1 kJ for octane).