When ammonium chloride crystals are dissolved in water, the temperature of the w
ID: 895169 • Letter: W
Question
When ammonium chloride crystals are dissolved in water, the temperature of the water decreases. The temperature change indicates that the solution process is (endothermic/exothermic) because the system (absorbs releases) heat. A system receives 575 J of heat and delivers 425 J of work. Calculate the change in the internal energy E of the system. Is the process endothermic or exothermic? Explain. A 275-g sample of nickel at 100.0 degree C is placed in 100.0 mL of water at 22.0 degree C in a coffee-cup calorimeter. What is the final temperature of the water? Assume that no heat is lost to or gained from the surroundings. Specific heat capacity of nickel and water are 0.444 J/(g K) and 4.184 J (g K) respectively. Arrange the following gases in order of increasing rate of effusion. Explain your answer. Nitrogen will behave most like an ideal gas at high temperature and high pressure at high temperature and low pressure at low temperature and high pressure at low temperature and low pressure at intermediate (moderate) temperature and pressure
Explanation / Answer
1. Here a decrease in the temperature of water inidicates that heat is absorbed by ammonium chloride while dissolution in water. When heat is absorbed, the reaction is called endothermic reaction.
Hence the temperature change indicates that the solution process is endothermic, because the system absorbs heat.
2. Given heat received by the system, Q = 575 J
Work done by the system, W = 425 J
Let the internal energy by DeltaH
According to first law of thermodynamics
Q = DeltaE + W
=> 575 J = DeltaE + 425 J
=> DeltaE = 575J - 425 J = + 150 J
Since DeltaE is positive, 150 J of the supplied heat is stored as internal energy and temperature of the system will increase. Hence the process is endothermic.
3. Let the final temperature of water be T DegC
Heat released by nickel = mxsxdT = 275 g x (0.444J/gxDegC) x (T - 100)
Heat absrbed by water = mxsxdT = 100.0 g x (4.184J/gxDegC) x (T - 22)
Applying law of calorimetry
Heat released by nickel + Heat absrbed by water = 0
275 g x (0.444J/gxDegC) x (T - 100) + 100.0 g x (4.184J/gxDegC) x (T - 22) = 0
=> 122.1T - 12210 + 418.4T - 9204.8 = 0
=> 540.5T - 21414.8 = 0
=> T = 21414.8 / 540.5 = 39.6 DegC.
Hence final temperature of water is 39.6 DegC (answer)
4. Rate of effusion is inversely proportional to square root of molecular mass. Hence lower molecular mass higher is the rate of effusion
C2H6 > PH3 > HCl > Ar
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