AP Chem 2012: FRQ #3c

<p>Just a quick question :)</p>

<p>I solved 3b and got a positive value, so obviously, the reaction would be endothermic.</p>

<p>So, I read the next part of the question and it asked about the change in temperature of the "contents" of the container. Unfortunately, I interpreted "contents" to mean the molecules of the container :/, not the actual container, itself :/</p>

<p>Is this ambiguous, or was I just being stupid :o? I'm leaning towards the latter XD</p>

<p>Actually, that is pretty ambiguous. When I was taking the test and even now, I thought it meant the temperature of the whole container, but since you bring it, I do recognize the ambiguity of the question.</p>

<p>Like, even me, I got a negative value. I said it was exothermic (yeah, I’m well aware my letter b was wrong, but I based my answer off letter b, so my c was right).</p>

<p>So I said it releases heat so therefore the insulated container temperature rises. But I can also see the ‘contents’ could have released the heat as well and and the contents decreased in temperature.</p>

<p>It’s quite ambiguously worded.</p>

<p>That’s how I interpreted it as well… I thought that since it was endothermic, it required energy, increasing the temperature of the molecules. Apparently, that’s not what they meant, or at least probably not, as most people in my class wrote that the temperature decreased.</p>

<p>Yeah, even though I got it right I didn’t like this question. Very needlessly ambiguous. Thankfully, I ran into a similar wording on a previous exam and knew to look out for such wording, as I originally interpreted ‘contents’ to mean the molecules themselves.</p>

<p>I don’t see the ambiguity?</p>

<p>“Contents” in this case could refer to either the molecules of the container or the space/air/system of the container itself.</p>

<p>Either interpretation would result in a different answer.</p>

<p>Can you explain the two possible answers?</p>

<p>If one interpreted the molecules themselves to be the “contents” of the container, they would have said that the molecules INCREASED in temperature, since the reaction was endothermic (or DECREASED, if they said that the reaction was exothermic).</p>

<p>If one interpreted the system/air of the insides of the container to be the “contents,” they would have said that the contents DECREASED in temperature, since energy would have to leave the area surrounding the molecules to fuel the reaction (or INCREASED, if they said that the reaction was exothermic - the opposite reasoning applies here).</p>

<p>

An endothermic process absorbs heat. Heat (energy) is absorbed in the process of breaking/making bonds.</p>

<p>Why do you think that “the molecules INCREASED in temperature” in this situation?</p>

<p>Because when you absorb heat, you get, for the lack of a better term, “hotter” which means the temperature goes up.</p>

<p>But also, when you absorb heat, you absorb it from the surroundings (system + surroundings = universe) and therefore you take the heat from the surroundings; the surroundings subsequently get colder and the container’s temperature decreases.</p>

<p>Make more sense now?</p>

<p>

Do you recall the difference between heat and temperature? :)</p>

<p>When heat energy is absorbed in an endothermic reaction, it is converted to chemical potential energy. Absolute temperature is proportionate to average molecular kinetic energy.</p>

<p>Your answer is correct…but I do not see the question as ambiguous.</p>

<p>I knew my answer was right.</p>

<p>But do we describe that actual THING inside the insulate container or the insulated container itself? That’s the ambiguity >.></p>

<p>Absorbing heat does not necessarily raise temperature. The heat energy is used to break bonds, not increase kinetic energy.</p>

<p>Uh, in terms of a COLLEGBOARD AP Chem problem, it actually does.</p>

<p>It’s as simple as knowing the difference between endothermic and exothermic.</p>