Name:______
Chapter 16 Quest (a)
Read each questions carefully, Show all your work including any equations you may use. Remember to label all answers with units and rounded to proper sig figs.
1. The temperature of a piece of copper with a mass of 95.4 g changes from 25.0°C to 48.5°C when the metal absorbs 849 J of heat. What is the specific heat of copper? (8 points)
2. Will the specific heat of a 50.0 g substance be the same as or greater than the specific heat of 10.0 g of the same substance? Why? (6 points)
- When two substances, water and copper (III) chloride, are mixed together, the glass beaker becomes cool to the touch. (4 pts)
a. Is this an endothermic or exothermic reaction?
4. 2NaHCO3(s) + O2 (g) Na2CO3(s) + H20(g) + CO2(g) DH = +129 kJ
Using the above equation calculate the kJ of heat required to decompose 2.24 mol of NaHCO3(s). (8 points)
5. When ammonia reacts with oxygen gas, nitrogen dioxide and water vapor are produced.
__NH3(g) + __O2(g) __NO2(g) + __H2O(g) ΔHº = ?
a. Balance the equation. (2 points)
b. Find the change in enthalpy (DH°f) for the above equation using the standard heats of formation (6 points)
ΔHºf NH3(g)= -46.19 kJ/mol
ΔHºf NO2(g) = 33.85 kJ/mol
ΔHºf H2O(g) = -241.8 kJ/mol
6. How much energy is needed to heat a 50.0g piece of ice from -20oC to 50oC? (hint…..did the ice melt?)
7. Use Hess’s law to find the DH for the formation of tungsten carbide from the steps provided below. Is this reaction ENDOTHERMIC or EXOTHERMIC? (8 points)
W(s) + C(s) à WC(s)
1) 2W(s) + 3O2(g) à 2WO3(s) DH = -1685.8 kJ
2) C(s) + O2(g) à CO2(g) DH = -393.5 kJ
3) 2WC(s) + 5O2(g) à 2WO3(s) + 2CO2(g) DH = -2391.8 kJ