Energy and Conservation
Supplemental Instruction
Iowa State University / Leader: / Sara
Course: / Chem177
Instructor: / Bonaccorsi
Date: / 2/24/14
1) If you mix 5.00 g solid Ag2S (mm=248) with 15.0 mL of .5 M NaCl, what are the products and how much solid is formed?
Ag2S + 2NaCl à 2AgCl(s) + Na2S(aq)
5.00 g / (248 g/mol) * 2mol/1mol = .0403 mol AgCl
.5 M * .015 L * 1mol/1mol = .0075 mol AgCl
.0075 mol AgCl produced
2)
3) What is the difference between a closed system, and open system and isolated?
Closed does not have mass transfer but has heat transfer
Open has both mass and heat transfer
Isolated does not have mass transfer nor heat transfer
4) Are the following are independent of path?
a. The potential energy of lifting a glass from the dishwasher to a shelf
b. The work involved in the combustion of butane
c. The heat used in turning glucose into H2O and other products
5) If 680 J of heat is added to a system and 7.2 kJ of work is done by the system what is the total internal energy?
+680 J -7.2kJ=.68-7.2= -6.5 kJ
6) 2 substances of equal mass and temperature are put in a pot of boiling water for the same amount of time. Their specific heats are .56 J/gK and 1.4 J/gK, which has a warmer final temperature?
The one with a specific heat of .56 J/gK b/c is takes less energy to warm up
7) In a calorimeter you have 231 mL of water at 19 degree Celsius. You put in a 76 g sample of titanium (specific heat = .54 J/gK). After a long time the final temperature of the water and metal is 29oC. What was the initial Temperature of the titanium?
qsol = -qsolid
mmetal x Csmetal x ∆Tmetal = -msol x Cssol x ∆Tsol
231 g * 4.184 J/gK * (10) = -76g * .54 J/gK*(29-T)
T=264 C
8) Titration review: If you titrate 40.3 mL of unknown concentrated Phosphoric acid with 30.9 mL of .89 M Barium Hydroxide. Find unknown concentration?
.89 mol/L * .0309 L * 2 mol H3PO4/3mol Ba(OH)2 / .0403 L = .4549=.45 M
9) Definitions to know
10) Energy: The capacity to do work or transfer heat
11) Work: the energy used to cause and object to move against a force
12) Heat: the energy used to cause the temperature of an object to increase.
13) Internal Energy: total energy in a system, kinetic and potential (∆E=q+w)