Enthalpies of Formation and Reaction

  __________________________states that if you add two or more thermochemical equations to give an overall equation, you can also add the enthalpies of reaction to give the overall enthalpy of reaction.

• The collision theory

•   Rutherford’s hypothesis

• Hess’s law of heat summation

• Bohr’s theory

Calculate the enthalpy of the following chemical reaction:

C(s) + O₂(g) + 2H₂O(g) → CO₂(g) + 2H₂(g) + O₂(g)

Given:

2H₂O(g) à 2H₂(g) + O₂(g)      ∆H = +483.6 kJ/mol 

C(s) + O₂(g ) à CO₂(g)             ∆H = ‒393.5 kJ/mol  

• 90.1 KJ/mol

• 100 KJ/mol

• 877.1 KJ/mol

• 967.2 KJ/mol

_______________________of a compound is the change in enthalpy when one mole of the compound is formed from its elements

•   Enthalpy of solution (ΔH_soln)

• Enthalpy of reaction (ΔH)

• Standard enthalpy of formation (ΔH_f°)

•   Thermochemical equation

The standard enthalpy of formation for a free element in its standard state is set at 25.

• True

• False

What is the standard enthalpy of reaction (ΔH°) for the reaction of SO₂(g) with O₂(g) to form SO₃(g)? 

2SO₂(g) + O₂(g) → 2SO₃(g)

Note: ΔH_f° of O₂(g) = 0.0KJ, ΔH_f° of SO₂ (g)= -296.8KJ, ΔH_f° of SO₃ (g)= −395.7KJ

• ‒197.8 kJ/mol

•    -791.4kJ/mol

• + 593.6kJ/mol

•     0.00kJ/mol

Breaking up the attractive forces within a compound (the solute) is____________________.

•   a physical change

• an exothermic process

• an endothermic process

• none of the above

 

In the exothermic process, the value of the enthalpy change is ______________________

•    Negative

• Positive

• Having no charge

• All of the above

When 1 mol of NaOH(s) is dissolved in water, 44.5 kJ of heat are released. How much heat is released when 4.2 mol of NaOH(s) is dissolved in water?

• -44.5 KJ

• -186.9 KJ

•   -10.59 KJ

• + 186.9KJ

How many moles of NH₄NO₃(s) must be dissolved in water so that 125 kJ of heat is absorbed from the water? ΔHsoln for the dissolution of NH₄NO₃(s) in water is 25.7 kJ/mol

• 25.7 mol

•   3.21 mol

•     4.86 mol

•     5 mol

The standard state is the stable form of a substance at a temperature of _____and a pressure of 100 kPa

• 25°C

•    35°C

• 45°C

•   55°C