1. Thermochemical Practice Problems
Section 11.1 and 11.2
Due Friday, Feb 13
Thermochemical Practice Problems

2. When 435 J of heat is added to 3
When 435 J of heat is added to 3.4 grams of olive oil at 21oC, the temperature increases to 85oC. What is the specific heat of olive oil?
Answer: 1.9 J / goC

3. How much heat (J) is required to raise the temperature of 250
How much heat (J) is required to raise the temperature of grams of mercury 52.0oC? The specific heat of mercury is in Table 11.2 on page 296 of your text
Answer: J

4. The heat involved in a reaction
What is enthalpy?
The heat involved in a reaction
a. Write the ∆H for a reaction that absorbs 125 kJ of heat.
∆H = 125 kJ
b. Write the ∆ H for a reaction that releases 125 kJ of heat.
∆H = kJ

5. 4. Watch this video clip
a. Is this reaction endothermic or exothermic?
Exothermic
b. Write the ∆H for this reaction if it transfers 900.kJ of heat.
∆H = -900 kJ

6. 5. During the electroysis of water, electrical energy is used to decompose water into hydrogen and oxygen gas. During this reaction, 241.8kJ of energy is added to the system from the surroundings.
Is this reaction endothermic or exothermic?
Write a thermochemical equation for this reaction using enthalpy (∆H).
2H2O(l)  2H2(g) + O2(g) ∆H = kJ OR
2H2O(l) kJ  2H2(g) + O2(g)

7. When 2 mol of solid Magnesium combines with 1 mol of oxygen gas, 2 mol of magnesium oxide is produced and 1204 kJ of heat is released. Write the thermochemical equation for this combustion reaction.
2Mg + O2  2MgO kJ OR
2Mg + O2  2MgO ΔH = kJ

8. 7. Hydrogen gas and fluorine gas react to produce hydrogen fluoride
7. Hydrogen gas and fluorine gas react to produce hydrogen fluoride. Calculate the heat change (in kJ) for the conversion of 15.0 grams of hydrogen fluoride gas at constant pressure. H2(g) + F2(g)  2HF(g) ∆H = -536 kJ Answer: -201 kJ