Chemistry
posted by Sarah on .
1) When hydrazine (N2H4) is burned in a 253g brick container, the temperature of the brick increases by 5.13 degrees Celsius. Calculate the quantity of heat released in this raection. The specific heat of brick is 0.840 J/(gC).
2) A sample of coal is burned in a bomb calorimeter with a heat capacity of 4.62 KJ/C. The temperature in the calorimeter rises from 20.22 to 25.25 degrees celsius. Calculate the heat of the combustion reaction (qrxn) in KJ.
How do I solve these problems?

q = mass brick x specific heat brick x delta T.
q = 4.62 kJ/C x delta T. 
When I solved it the second problem it had a positive sign (23.2 KJ). Is that right or wrong because the problem wants heat of combustion?

#1. You are calculating the heat from heating bricks when N2H4 burns. You get a positive number because you are adding heat to the bricks; that is the same as the heat RELEASED by burning N2H4. Delta H for burning N2H4 is (heat released) negative.
#2. You are burning coal. The water absorbs the heat (same as the bricks in #1) so q comes out to be positive. However, the coal RELEASED heat so delta H for the combustion is negative. 
Drbob you are wrong i got the question wrong doing what you told me to