A) Which of These Processes Is Endothermic?

Leader: Lauren Ch 9 Course: Chem 167 Supplemental Instruction Instructor: Holme Iowa State University Date: 10/21/09

1. The contents of the closed box in each of the following illustrations represent a system, and the arrows show the changes to the system during some process. The lengths of the arrows represent the relative magnitudes of q and w. a) Which of these processes is endothermic? b) For which of these processes, if any, is ∆E<0? c) For which process, if any, is there a net gain in internal energy?

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2. a) State the first law of thermodynamics.

b) What is meant by the internal energy of a system?

c) By what means can the internal energy of a system increase?

3. Calculate ∆E, and determine whether the process is endothermic or exothermic for the following cases:

a) a system absorbs 85 kJ of heat from its surroundings while doing 29 kJ of work on the surroundings.

b) q=1.50 kJ and w = -657 J.

c) the system releases 57.5 kJ of heat while doing 13.5 kJ of work on the surroundings.

Supplemental Instruction 1060 Hixson-Lied Student Success Center v 294-6624 v www.si.iastate.edu 4. Ethanol (C2H5OH) melts at -114⁰C. The enthalpy of fusion of ethanol is 5.02 kJ/mol. The specific heats of solid and liquid ethanol are 0.97 J/g-K and 2.3 J/g-K, respectively. How much heat is required to convert 75.0 g of ethanol at -120 ⁰C to the liquid phase at 68⁰C?

5. What is a ‘state function’?

6. When a 9.55 g sample of solid sodium hydroxide dissolves in 100.0 g of water in a calorimeter, the temperature rises from 23.6⁰C to 47.4⁰C. Calculate ∆H (in kJ/mol NaOH) for + - the solution process: NaOH(s) Na (aq) + OH (aq) . Assume that the specific heat of the solution is the same as that of pure water (4.184 J/g-K).