ws4s08key - CH 302 Spring 2008 Worksheet 4 Answer Key...

Info iconThis preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon
CH 302 Spring 2008 Worksheet 4 Answer Key Practice Exam 1 1. Predict the signs of Δ H and Δ S for the sublimation of CO 2 . a. Δ H > 0, Δ S > 0 b. Δ H > 0, Δ S < 0 c. Δ H < 0, Δ S > 0 d. Δ H < 0, Δ S < 0 Answer: This reaction happens only at higher temperatures, which means Δ H > 0 and Δ S > 0. 2. Vapor pressure increases ________ with temperature. a. Linearly b. Exponentially c. Logarithmically d. Quadratically Answer: Recall the Clausius-Clapeyron equation. Pressure is related exponentially to temperature. 3. Which of the following salts will dissolve most easily in water? a. LiF b. MgO c. BN d. KBr Answer: The salt with the lowest charge density will dissolve the easiest. BN and MgO both have multiple charges, so they have high charge density. Li+ and F- are smaller than K+ and Br-, so LiF has a higher charge density than KBr.
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
4. For this question, refer to the phase diagram shown above. What is the phase of this substance at -56°C and 5.1 atm? a. Solid b. Liquid c. Gas d. Mixture of solid and gas e. Mixture of solid, liquid, and gas f. Supercritical fluid Answer: This is the triple point, which is the point at which solid, liquid, and gas are all at equilibrium with each other. 5. For this question, refer to the phase diagram shown above question 4. The substance is originally held in a container at -60°C and 20 atm. It is then heated to room temperature, and next allowed to expand to atmospheric pressure. What happens to the substance? a. The liquid in the container boils. b. The liquid in the container becomes a supercritical fluid. c. The gas in the container becomes a supercritical fluid. d. The solid in the container sublimes. e. The solid in the container melts, then the resulting liquid boils. f. The solid in the container sublimes, and then the resulting gas condenses. Answer: Just trace the two steps on the phase diagram. 6. 1 kg of water starts at 200°C and is allowed to cool to room temperature. For water, the specific heats are c ice = 2.093 J/g°C, c water = 4.186 J/g°C, and c steam = 2.009 J/g°C. The enthalpy changes are Δ H fusion = -335.5 J/g and Δ H vaporization = 2.26 kJ/g. What is Δ H sys for this process? a. -2775 J b. -2775 kJ c. +2775 kJ d. -1745 kJ e. +1745 kJ Answer: Divide the process into three stages. Cool steam 200°C 100°C: H = mc steam T = (1000g)(2.009 J/g°C)(-100°C) = -201 kJ Condense steam: H = m H melting = -m H vaporization = (1000 g)(2.26 kJ/g) = -2260 kJ Cool water 100°C 25°C: H = mc water T = (1000g)(4.186 J/g°C)(-75°C) = -314 kJ H tot = -201 kJ + -2260 kJ + -314 kJ = -2775 kJ
Background image of page 2
7. Which of the following gases will be most soluble in water? a.
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 4
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 04/12/2008 for the course CH 302 taught by Professor Holcombe during the Spring '07 term at University of Texas at Austin.

Page1 / 9

ws4s08key - CH 302 Spring 2008 Worksheet 4 Answer Key...

This preview shows document pages 1 - 4. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online