midyear0506 exam

midyear0506 exam - CHEM 1000 A and V Exam December, 2005...

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CHEM 1000 A and V Exam December, 2005 Part A. 60 marks. Answer each question (5 marks each). 1. Write the net ionic equation for the reaction 2 AgNO 3(aq) + PbCl 2(aq) → 2 AgCl + Pb(NO 3 ) 2 Ag + (aq) + Cl - (aq) → AgCl (s) 2. State whether or not each of the following processes or reactions is spontaneous as written: 2 Li (s) + Pt +2 (aq) 2 Li + (aq) + Pt (s) Yes (Li is above Pt in the activity series Sn +2 (aq) + Co (s) Sn (s) + Co +2 (aq) Yes (Co is above Sn is the activity series) 2 H + (aq) + Hg (l) H 2(g) + Hg +2 (aq) No (Hg is below H 2 in the activity series) CH 4(g) + 2 O 2(g) CO 2(g) + 2 H 2 O (g) Yes (This is a combustion reaction, H<0, S 0, thus G<0 H 2 O (g) H 2 O (l) at 95 o C No (The temperature is below the boiling point of water) 3. What type of hybrid orbitals does the Se atom use in a molecule of SeCl 2 ? This is of the form AX 2 E 2 . There are thus four electron clouds around the Se atom, which must therefore be using sp 3 hybrid orbitals. 4. Explain the term “effective nuclear charge” and use it to explain why the ionization potential increases going left to right across a period. Effective nuclear charge is a measure of how strongly the nucleus attracts the valence electrons. Going left to right across a period, electrons are being added the same principle shell. They therefore do not shield each other very effectively. Also, protons are being added to the nucleus, with the result that the effective nuclear charge increases, and thus the ionization potential increases. 5. A reaction has a positive value of H and a negative value of S. Will this reaction be spontaneous at high temperature, low temperature, both or neither? How do you know? G = H - T S. If H > 0 and S<0, then G will be positive at all temperatures, i.e. the reaction will not be spontaneous at any temperature. 6. Why is the O 2 molecule paramagnetic? This is because the molecule has two unpaired electrons in its highest energy molecular orbital. 7. Why is the ‘V’ in the ideal gas equation replaced with ‘V-nb’ in the van der Waals equation? The gas molecules themselves actually take up some of the volume of the container, so the volume that any one molecule has to fly around in is actually less than V. n is the number of moles of gas and b is a measure of the size of the molecules, both of which reduce the volume from V to a lower value. 8. Does the position of the equilibrium in the reaction 2 H 2(g) + O 2(g) 2 H 2 O (g) shift left or right when we: Increase the pressure Right Increase the temperatureLeft Add some H 2 O (g) Left Remove some O 2(g) Left
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Chemistry 1000 A and V Mid-Year Examination, December, 2005 Page 2 of 8 Add an inert gas such as N 2(g) Can not tell without knowing if the volume changes or not. Everyone gets one mark for this one! 9.
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midyear0506 exam - CHEM 1000 A and V Exam December, 2005...

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