Department of Chemistry Brooklyn College Chemistry I; Summer 2017 Exam IIIB Name

Question

Department of Chemistry Brooklyn College Chemistry I; Summer 2017 Exam IIIB Name: 01.(9 pts, 2 pts each) True (T) or false (F) ? a AE(system) + AEX surroundings)-0 b. If the chemical reaction is exothermic, the temperature of the surroundings c. If the heat is transferred from the system to the surrounding and the work is dome k is done by the system on the surroundings, AE> O ing processes, P-coms 2. ( (6 pts) Indicate the sign of the enthalpy change, AH, in each of the following a I g of C2He is burned in oxygen a. I mL of water evaporates of t of 0.100 M solution of NaBrag), which one (d) none of the above oI G pts) IE'we add 30 mL of pure water to 30 mL following parameters will not change? (select one) (a) the number of moles of NaBr (b) volume (e) molarity #4. (3 pts) Box 1 contains H2(g) and Box 2 contains N2(g) Both boxes are held at the same constant temperature of 25°C. Which one of the following statements is true? (select one) (a) The molecules in Box 1 travel at many different speeds and the average speed in Box 1 is greater than the average speed in Box 2. (b) The molecules in Box 1 travel at many different speeds and the average speed in Box 1 is less than the average speed in Box 2. (e) The molecules in Box I travel at many different speeds and the average speed in Box 1 is the same as the average speed in Box 2 (d) All the molecules in Box I travel at the same spced and this speed is greater than the speed of (e) () All the molecules in Box 1 travel at the same speed and this speed is the same as molecules in Box 2. All the molecules in Box 1 travel at the same speed and this speed is less than the speed of molecules in Box 2 speed is the same as the speed of molecules in Box 2 5. (3 pts) Which of the following gasses has the lowest average molecular speed at 300 K? (a) N2 (b) H (c) Co. (d) all three of these gasses have the same average have the same average molecular speed at 300 K

Explanation / Answer

1. a) It is a false statement since the entropy of a system is always greater than zero.

b) False, in exothermic reactions energy is released, so the temperature of the surrounding increases.

c) False, since symbol of dH<0 and dW>0;

since, dH= dE + dW

so dE= dH - dW <0

Thank you

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