1. Identify if the energy exchange is work or heat. a. b. c. d. A ball rolling d
ID: 1042616 • Letter: 1
Question
1. Identify if the energy exchange is work or heat. a. b. c. d. A ball rolling down a hill Water turning a turbine in a hydroelectric power plant Water being converted to steam in a coal burning power plant A beverage chilling in a refrigerator 2. The average adult male taking a deep breath (inspiratory capacity) expands the lungs by about 3.8L. If this expansion occurs against an atmospheric pressure of 1 atm, how much work is done during the expansion? (Useful conversion factor 1 atm*L 101 J) What mass of natural gas (CH4) must burn to produce 100kJ of energy? CH4(g)2 O2(g)CO2(g)2 H20(g) 50g of ethanol (CH3CH2OH) at 30°C is mixed with 375g of water at 2°C. What is the final temperature of the mixture? Many ionic solids release heat when they dissolve in water and the solution gets warm. Sodium nitrate is unusual in thatis absorbs heat chilling the solution when it dissolves. This property is used for instant cold packs NaNO3(s) Na (aq)NO3 (aq) If 50g of NaNO3 is dissolved in 500g of 25.3°C water, what will the final temperature of the solution be? Ignore heat capacity of NaNO3. 3. AHon-802.3kJ/mol 4. 5.Explanation / Answer
1.
(a) WORK
(b) WORK
(c) HEAT
(d) HEAT
2.
Work done , W = Pext * ( V2 - V1 )
W = 1.00 * ( 3.8 )
W = 3.8 L.atm
W = 3.8 * 101 J
W = 383.8 J
3.
802.3 kJ of heat is released from 16.0 g. of methane
Then, 100 kJ of energy ie released from 100. * 16 / 802.3 = 1.99 g. of methane
4.
q = mass * specific heat * change in temperature
50 * 2.46 * ( t2 - 30 ) + 375 * 4.184 * ( t2 - 2 ) = 0
123*t2 - 3690 + 1569*t2 - 3138 = 0
1692 * t2 = 6828
t2 = Final temperature = 4.04 0C
5.
Molar mass of NaNO3 = 23 + 14 + 3 ( 16 ) = 85.0 g/mol
Heat absrobed by 50 g. of NaNO3 solution = 50 * 26. / 85 = 15.3 kJ = 15300 J
Heat change = mass * specific heat * change in temperature
15300 = - 500 * 4.184 * ( t2 - 25.3 )
t2 - 25.3 = - 7.31
t2 = final temperature = 18.0 0C
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