SUCCEEDING IN THE VCE 2017 UNIT 3 CHEMISTRY STUDENT SOLUTIONS

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1 SUCCEEDING IN THE VCE 017 UNIT CHEMISTRY STUDENT SOLUTIONS FOR ERRORS AND UPDATES, PLEASE VISIT QUESTION 1 The word "released" takes the negative sign into consideration. Answer must be positive. From the given equation: 1 e releases 890 kj of energy, therefore, e will release twice the amount = 1780 kj Answer = kj (b) 8 n methane e releases 890 kj of energy. 0.5 e releases half the value kj 445 kj would be released. QUESTION oxygen) 8516 oxygen) oxygen) g The School For Excellence 017 Succeeding in the VCE Unit Chemistry Page 1

2 (b) n CO ( ( m CO ) ) g 1.95 kg E 5.5 E kj kj kj of energy was released QUESTION E(J) mct J kj 4. kj QUESTION 4 E(J) mct E(J) 0, 000 o T.9.4 C mc The School For Excellence 017 Succeeding in the VCE Unit Chemistry Page

3 QUESTION CH 8) E J 6.7 kj Heat of 6.7 Combustion kj 1 (b) Not all of the energy from the propane is transferred to the water, some is lost as heat and is not accounted for in the calculations making the ar heat of combustion lower than it should be. (If all of the energy was transferred, the temperature of the water would increase by a larger amount.) (c) (d) Insulate the beaker. Place the beaker close to the flame. Make sure there is a good supply of oxygen to ensure complete combustion. Place a cover over the beaker. Distance between beaker and flame. Size and shape of the beaker. Amount of insulation. Same cover for beaker. Same rate of stirring (if stirred). Same volume of water. Same amount of gas. If the energy transfer was 100% efficient and the water was 100% insulated then the amount of fuel and amount of water should not matter since this would all be taken into account in the calculations. However, these two conditions are never going to be met! A smaller volume of water will have a larger surface area to volume ratio which could affect the rate of cooling. Therefore, the volume of water used should stay the same. The amount of fuel should also stay the same to avoid other experimental errors. For example, heating rates may not be constant as a fuel is burnt. So if one fuel burns longer than another, this could introduce error. Some of these errors may be unavoidable since burning one e of each gas doesn t mean that they will burn for the same amount of time. However, hopefully if there are not huge differences in the amount/volume/mass burning, then these errors can be minimised. The School For Excellence 017 Succeeding in the VCE Unit Chemistry Page

4 QUESTION g E released E released kj E mc E mc C Take into account the 80% efficiency: C The School For Excellence 017 Succeeding in the VCE Unit Chemistry Page 4

5 (b) If 100% efficient: E mc J 09 kj Take into account the inefficiency: 80 x x kj g The School For Excellence 017 Succeeding in the VCE Unit Chemistry Page 5

6 QUESTION 7 QUESTION 8 QUESTION 9 QUESTION 10 QUESTION 11 QUESTION 1 QUESTION 1 QUESTION 14 QUESTION 15 QUESTION 16 QUESTION 17 QUESTION 18 QUESTION 19 Answer is A Answer is B Answer is B Answer is B Answer is C Answer is A QUESTION 0 PV T nrt PV nr K C QUESTION 1 PV nrt PV n RT The School For Excellence 017 Succeeding in the VCE Unit Chemistry Page 6

7 QUESTION (b) 10% of the fuel is ethanol 7.00 L ethanol) g 55 ethanol) CO) PV nrt nrt V P (5 7) L (c) Yes if the ethanol was sourced from fossil fuels since no carbon dioxide is removed from the atmosphere by its production or combustion. No if the ethanol was sourced from biomass. In this case, some of the carbon dioxide released would be offset by the carbon dioxide absorbed when the crop was growing. The School For Excellence 017 Succeeding in the VCE Unit Chemistry Page 7

8 QUESTION Conditions were not held constant so the heat of combustion would turn water into a gas. This is a limiting reactant question so find the e of both reactants: CHOH) Use initial conditions to determine the amount of oxygen that was present: O ) 8.1 (7 ) 0.8 Determine which reactant is limiting: CHOH ) : O ) : : 0.17 Oxygen is the limiting reactant. Both carbon dioxide and water are greenhouse gases use the e of oxygen to find the amount of both these gases. CO ) O ) CO) g 4 H O) O ) m H O) ( g greenhouse gases) g The School For Excellence 017 Succeeding in the VCE Unit Chemistry Page 8

9 (b) What mass of greenhouse gas is produced per unit of energy? 1 State your answer in g kj. H c ( CHOH) 75 kj 1 CH OH( l ) O( g) CO( g) 4HO( g) 1450 kj Oxygen is the limiting reactant so use n O ) to find the energy that would be released. E E released kj Greenhouse gases emitted: 0.4 Greenhouse gases emitted g kj ( 1 1 The School For Excellence 017 Succeeding in the VCE Unit Chemistry Page 9