# Did you get a 5 for AP Chem??

<p>Well then, I need help...(easy for you, challenging for me)</p>

<p>1.- When a large amount of ammonium chloride is added to water at 25 Celsius, some of it dissolves and the temperature of the system decreases. Predict how the enthalpy changes in the system during the process. Explain the basis for your prediction.(need help)</p>

<p>2.-Propane, C3H8, is a hydrocarbon that is commonly used as fuel for cooking.
a)Balanced EQ: C3H8 + 5O2 --> 4H2O + 3CO2 (I did this)
b)Heat of formation: -(-2220.1+0)+(4(-285.3)+3(393.5))= 2259.4 kj (I did this)
c) Assuming that all of the heat evolved in burning 30 gr. of propane is transferred to 8kg of water (specific heat-4.18 J/g*C), calculate the increase in temperature. (need help)</p>

<ol>
<li>temperature of system decreases because it took in heat from its surroundings, which means that the reaction was endothermic, so the delta H (change enthalpy) is positive.</li>
</ol>

<p>don't feel like getting out my calculator and doing the 2nd problem :)</p>

<p>lol.. oh geez, i cant do it.. my motivation to get a five was so i would never have to look at chemistry again.</p>

<p>Thanks athlon...I thought about that first....so, I am not that lost....
I think the same way ranisparkle....</p>

<p>for c, just "match the units"</p>

<p>Thanks...I will try that</p>

<p>This is kinda irrelevant...but don't worry too much about the chemistry test...just study the Princeton review for tests and look at APCliffs Chemistry for labs</p>