i have some questions.. i just took an AP chem test and did bad, so now i am doing test corrections.. HELP!!!

Question

here are my questions..
Consider the following reaction:
2Al(s) + 3Cl2(g) ---> 2AlCl3(s) deltaH = -1390.81

a. Calculate the heat produced when 10 grams of AlCl3 forms?
b. How many grams of Al are required to produce 1.00 kJ of energy?
xxxx
The heat of combustion for a sample of coal is 23.0 kJ/g. what quantity of this coal must be burned to heat 500.0g of water from 20(degrees Celcius) to 90(degrees celcius)?
xxxx
if 5.0 kJ of energy is added to a 15.5g sample of water at 10(degrees celcius) the water is still a liquid. Why?
xxxx
you have a 28.2g sample of a metal heated to 95.2(degrees C). the final temperature of the water is 31(degrees C. assuming no heat is lost to the surroundings nor the calorimeter, calculate the heat capacity of the metal.

I WOULD APPRECIATE YOU IF SOMEONE COULD HELP ME FIGURE OUT WHAT I AM DOING WRONG!
just letting you know i am in HS not college! i would appreciate knowing the correct answers so i wont have to repeat this class in college!

Answer 1

the delta H is KJ per mole and is exothermic.

Since you are in AP, I assume you know about moles.

calculate moles of AlCl3 and multiply by delta H to get part a

For part b, its the reverse calculation. You want 1 KJ and the delta H is for a full mole. Divide 1 / 1390.81 x mol mass and you have the grams.

For part c, liquid wat Cp is 4.814 j/g. You have 15.5 g of water. Calculate how many joules to raise this mass of water by 1 oC. You are adding 5,000 j of energy. Is it enough to get the water to the boiling point?

The last one uses the equation q = mCp delta T. I am sure you solved these in your first year course. Set the heat gain of the water equal to the heat loss of the metal and solve for Cp of the metal

Answer 2

You can just take it, just to see how you're going to do. It won't affect anything right? Nobody has died from taking a test :P