Data: ?Hf values: CH4(g), -74.8 kJ; CO2(g), -393.5 kJ; H2O(l), -285.8 kJ. Using
ID: 744596 • Letter: D
Question
Data: ?Hf values: CH4(g), -74.8 kJ; CO2(g), -393.5 kJ; H2O(l), -285.8 kJ. Using the ?Hf data above, calculate ?Hrxn for the reaction below. Reaction: CH4(g) + 2O2(g) => CO2(g) + 2H2O(l)Explanation / Answer
K I just finished my webassign hw. 1. The answer I got was -373.3 The way I got that was multiply the CO + 1/2 O2 equation by 2. This will give you: 2CO + O2 -> 2CO2 ?H = 2(-283.0) = -566 Now reverse the other equation so it is: 2NO -> N2 + O2 ?H = (-) 180.6 negative because its reversed. So the O2's cancel. Add the two equations together: 2CO + 2NO -> 2CO2 + N2 ?H = -746.6 divide everything by 2. Thats how I got my answer. 2. This one have me stumped too. The answer I got was 115.6 87.9 + 27.7 = 115.6 Not too sure y you add. Im behind in reading. 3. I got this one wrong. But what I did was reversed the middle equation then added the equations. I forgot to add in N2 so that might be where I went wrong. By the time I figured it all out I had used up my 3 tries. 4. (a) -433.8 Ill show you how to do (a) since thats the same equation I got on my webassign. balance the equation. CH4 + Cl2 -> CCl4 + 4HCl CH4 = -74.9 CCl = -139.5 Cl2 = 0 HCl = -92.3 *If you are using the Chemistry Silberberg book (fifth edition) you can find these values in appendix B. If not then there are some great sites that can help you find heat formation. well we use the products - reactants. (-139.5 + 4(-92.3)) - (-74.9) = -433.8 This is also why it is important to know what is gas, liquid, or solid. The ?H depends on that.
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