1) When hydrazine (N2H4) is burned in a 253-g 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
To solve these problems, we need to use the equation Q = m * c * ΔT, where Q is the quantity of heat released or absorbed, m is the mass, c is the specific heat, and ΔT is the change in temperature.
1) For the first problem, we need to find the quantity of heat released when hydrazine is burned in the brick container.
We are given:
- Mass of the brick container (m) = 253 g
- Change in temperature (ΔT) = 5.13 °C
- Specific heat of the brick (c) = 0.840 J/(g°C)
Using the equation Q = m * c * ΔT:
Q = 253 g * 0.840 J/(g°C) * 5.13 °C
Q ≈ 1091.7 J
Therefore, the quantity of heat released in this reaction is approximately 1091.7 J.
2) For the second problem, we need to find the heat of the combustion reaction (qrxn) when coal is burned in the bomb calorimeter.
We are given:
- Mass of the coal burned (m) = Not given.
- Change in temperature (ΔT) = 25.25°C - 20.22°C = 5.03 °C
- Heat capacity of the bomb calorimeter (c) = 4.62 kJ/°C
First, we need to convert the heat capacity from kJ to J by multiplying it by 1000:
c = 4.62 kJ/°C * 1000 J/kJ = 4620 J/°C
Now, we can rearrange the equation Q = m * c * ΔT to solve for mass (m):
Q = m * c * ΔT => m = Q / (c * ΔT)
Substituting the given values:
m ≈ Q / (4620 J/°C * 5.03 °C)
Since we are not given the quantity of heat released (Q), we cannot calculate the mass and therefore cannot directly find the heat of the combustion reaction (qrxn) in kJ.
To determine the heat of the combustion reaction, we need either the mass of the coal burned or the quantity of heat released during the combustion.