Chemistry Endo/exo

<li> Each of two solutions are mixed separately, and both solutions are found to be the same temperature. The two solutions are mixed, and a thermometer shows that the mixture’s temperature has decreased in temperature. Which of the following statements is true?
(A) The chemical reaction is exothermic.
(B) The chemical reaction is absorbing energy.
(C) The chemical reaction is releasing energy.
(D) The energy released could be found by multiplying the temperatures together.
(E) The energy absorbed by the solution is equal to the difference in temperature of the solutions. </li>
</ol>

<p>The answer is B. I don’t understand why. If its getting colder, doesn’t that mean its releasing energy and heat hence it is exothermic? Yet Sparknotes tells me that it is endothermic. This is the second time sparknotes has had a question like this and the answer is always opposite to what I thought it was. Can someone explain this?</p>

<p>When the reaction absorbs heat, it is endothermic ("endo-" means "inside" so you can think of the heat as flowing in) . When it releases heat, it is exothermic (similarly, "exo" means "outside" so you can think of the heat as flowing out). When you place a thermometer in a mixture in which an endothermic reaction is occurring, the temperature will decrease. This is because the reaction is absorbing energy from the surroundings and therefore since the surroundings contain less energy, it has a lower temperature. When an exothermic reaction occurs, it releases energy into the surroundings giving it a greater temperature.</p>

<p>^^^that was even more confusing!</p>

<p>What I'm putting below is simplified so that it's easier for you to understand</p>

<p>Exothermic: the bonds are breaking, so all the stored energy in those bonds is being released as heat (which would make the solution heat up)</p>

<p>Endothermic: the energy from the reaction is being stored into bonds that it is making(not breaking in exothermic reactions), so instead of heating up like in exothermic reactions, it is cooling down.</p>

<hr>

<p>You can think this way:</p>

<p>The chemical bonds are like the bank
Energy is like money</p>

<p>In an exothermic reaction, you're taking all the money out of the bank and you're RICH (hot) (but poor in the bank)
In an endothermic reaction, you're storing all your money into the bank, so you're poor (poor) (but rich in the bank)</p>

<p>If you're rich in the bank, you have the POTENTIAL to be rich outside of the bank (the potential is seen by the chemical bonds)
If you're poor in the bank, you DO NOT have the potential to be rich outside of the bank (if you already broke your bonds, you're poor in the bank)</p>

<p>i didn't read the posts above me but i had difficulty with this same problem. this is now how i think about it.</p>

<p>ok so the temperature of the system decreases right? that means that heat had to be absorbed into something, which is in this case the reaction. If one part loses energy, the other has to absorb it.</p>

<p>
[quote]
When the reaction absorbs heat, it is endothermic ("endo-" means "inside" so you can think of the heat as flowing in) . When it releases heat, it is exothermic (similarly, "exo" means "outside" so you can think of the heat as flowing out). When you place a thermometer in a mixture in which an endothermic reaction is occurring, the temperature will decrease. This is because the reaction is absorbing energy from the surroundings and therefore since the surroundings contain less energy, it has a lower temperature. When an exothermic reaction occurs, it releases energy into the surroundings giving it a greater temperature.

[/quote]
</p>

<p>This seems strange to me. Why is the temperature of the solution dependent on the surrounding energy?</p>

<p>I am rationalizing it that if it is endothermic then it is absorbing heat energy which should cause the temperature to increase. yet this is not the answer. Can somebody offer a better explanation or restate this explanation more clearly?</p>

<p>uhm, can it be that sparknotes got the answer wrong? i mean, the temperature of the mixture decreased, so IF the reaction was absorbing heat energy, then where is all that heat energy channeled to? the heat energy still remains WITHIN the mixture, so if the reaction were to be endothermic, the temperature would increase, not decrease.</p>

<p>and also, can anyone explain why Na+ is a conjugate acid of NaOH, i am SO confused with PR's explanation- if a conjugate base was to be one H+ lesser than a conjugate acid, then Na+ shld be a conjugate base right?! and also, why is it that the buffer equation:</p>

<p>pH = pKa + log [conjugate acid/conjugate base] be equivalent to</p>

<p>pH = pKa + log [A-/HA-];</p>

<p>isn't A- the conjugate base since it lacks a H+?! and HA- the conjugate acid since it has an extra H+?!</p>

<p>i dont know about Na+, but 'Na' is the conjugate acid of NaOH... think of 'Na' as Na (H20)...that way it's easy to see how Na is the conj acid of NaOH( it has one hydrogen atom more).......
hope that helps</p>

<p>well an endothermic reaction absorbs heat, so i like to think of an ice cube for this. you have a hot cup of tea, so you some ice cubes in it. the ice absorbs some of the heat, and cools down the tea. that's sorta how an endothermic reaction works. hope this helped =]</p>

<p>that's one way to look at it. . but still how are we supposed to know if the mixture's decrease in temperature can be attributed to an 'internal' endothermic process taking place or a simple exothermic process?</p>

<p>According to wiki, 'When using a calorimeter, the change in heat of the calorimeter is equal to the opposite of the change in heat of the system. This means that when the medium in which the reaction is taking place gains heat, the reaction is exothermic.'
Dunno how it's like with thermometer.</p>

<p>I was confused with this question until I read more about it. This of it like this: the new mixture is altering its intramolecular bonds by gaining energy. This energy is being taken from the outside mixture (energy in the form of heat) to the intramolecular bonds (energy in a DIFFERENT FORM). You are thinking it of as heat energy traveling from one medium to the next. This is not the case; the heat energy is changing form. You should think of it as energy, in the form of heat, traveling inside of the molecule to be changed into another form of energy that will be used to alter the bonds. It is absorbing outside heat energy and turning it into another form of energy. This means that it will become cooler, but still gain energy. The energy gained, however, is not longer in the form of heat. Thus, it cools down (but still gains energy).</p>

<p>Also: the molecule is gaining potential energy. The kinetic, heat energy from the surrounding environment is being converted into potential, different energy in the molecular bonds.</p>