Midterm #1 Answers - Name_ Chemistry 1A, Fall 2007 KEY...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
Name________________ Page 1 of 6 Chemistry 1A, Fall 2007 KEY Midterm Exam #1 September 18, 2007 (90 min, closed book) Name:__________________________________ SID:___________________________________ GSI Name:________________ The test consists of 4 short answer questions and a page of multiple choice questions. Put your written answers in the boxes provided. Answers outside the boxes may not be considered in grading. Write your name on every page of the exam. Question Page Points Score Question 1 2 19 Question 2 3 20 Question 3 4 16 Question 4 5 17 Multiple Choice 6 8 Total 80 Useful Equations and Constants: PV = nRT () nRT nb V V n a P = + 2 2 2 1 mv KE = P total = P A + P B = X A P A ° + X B P B ° N 0 = 6.02214 x 10 23 mol -1 T (K) = T (°C) + 273.15 R = 0.0821 L atm K -1 mol -1 1 atm = 760 mm Hg = 760 torr 1 bar
Background image of page 1

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

View Full DocumentRight Arrow Icon
Name________________ Page 2 of 6 Question 1, Gases (19 points total) Ammonia and trifluorobromide react according to the balanced equation given below. NH 3 (g) + BF 3 (g) NH 3 BF 3 (s) a. Complete the table below for the reactant molecules. NH 3 BF 3 Lewis Structure H N H H F B F F Name of Electron Pair Geometry tetrahedral trigonal planar Name of Molecular Geometry trigonal pyramidal trigonal planar Formal charge on central atom 0 0 b. Draw the Lewis structure of the product, NH 3 BF 3 . Why would these two molecules tend to react? In the forming the product the boron now attains an octet Consider an experiment where the two gas phase reactants are held at room temperature in separate flasks. The flasks are connected by a narrow tube with valves to control the flow of gas. c. On average, which sample of gas molecules is traveling at a greater velocity? NH 3 B F 3 both are the same d. If the valves were opened simultaneously and the gases reacted, predict approximately where in the tube would the solid form. Circle the position and show your calculation below. ) 3 ( 2 ) 3 ( 2 2 1 2 1 NH BF mv mv = 2 0 . 17 8 . 67 ) 3 ( ) 3 ( ) 3 ( ) 3 ( = = = NH BF BF NH MM MM v v so the NH 3 should travel twice as far as the BF 3 . The solid should form about 2/3 down the tube from the NH 3 .
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 6

Midterm #1 Answers - Name_ Chemistry 1A, Fall 2007 KEY...

This preview shows document pages 1 - 3. Sign up to view the full document.

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