A studen is asket to calculate the amount of heat involved in changing 10.0 g of liquid bomine at room temperature (22.5 C) to vapor at 59.0 C. To do this, one must know specific heat (0.474 J/g*C), boiling point (59 C), and heat of vaporization (29.6 kJ/mol) of bromine.In addition, the following step-wise process must be followed.
a) Calculate delta H for: Br2 (l, 22.5 C) --> Br2 (l, 59.0 C)
b) Calculate delta H for: Br2 (l, 59.0 C) --> Br2 (g, 59.0 C)
c) Using Hess's law, calculate delta H for: Br2 (l, 22.5 C) --> Br2 (g, 59.0 C)
I don't understand how you do (b), I got 173kJ for (a) and I understand Hess's law for (c), but (b) I really don't understand (b)
Since its a phase change in part b you have to calculate the delta h vap so in order to do that convert the 10 grams to mols then convert that to kj. ( delta h vap for one mole of br2= 29.6 kj). So 10 g / 159.80 x 29.6 kj = 1.85 kj
What about the c part
To calculate the amount of heat involved in changing 10.0 g of liquid bromine at room temperature (22.5 °C) to vapor at 59.0 °C, we need to follow the step-wise process and use the given information.
a) Calculate delta H for: Br2 (l, 22.5 °C) --> Br2 (l, 59.0 °C)
To calculate the heat involved in changing the temperature of liquid bromine, we can use the formula:
q = m * c * delta T
Where:
q = heat absorbed or released
m = mass of the substance (10.0 g)
c = specific heat capacity of the substance (0.474 J/g°C)
delta T = change in temperature (59.0 °C - 22.5 °C = 36.5 °C)
Plugging the values into the formula, we can find q:
q = 10.0 g * 0.474 J/g°C * 36.5 °C
b) Calculate delta H for: Br2 (l, 59.0 °C) --> Br2 (g, 59.0 °C)
To calculate the heat involved in the phase change from liquid to gas at the same temperature, we can use the formula:
q = m * delta H_vap
Where:
q = heat absorbed or released
m = mass of the substance (10.0 g)
delta H_vap = heat of vaporization of the substance (29.6 kJ/mol)
First, we need to convert the mass of bromine from grams to moles. The molar mass of bromine (Br2) is approximately 159.808 g/mol. Therefore:
moles = mass / molar mass = 10.0 g / 159.808 g/mol
Now we can calculate q:
q = (10.0 g / 159.808 g/mol) * 29.6 kJ/mol
c) Using Hess's law, calculate delta H for: Br2 (l, 22.5 °C) --> Br2 (g, 59.0 °C)
Hess's law states that if a chemical reaction can be expressed as the sum of two or more other reactions, then the heat of the overall reaction is the sum of the heats of the component reactions.
In this case, we can calculate delta H by adding the heat changes from parts a) and b):
delta H = delta H_a + delta H_b
So, plug in the calculated values from parts a) and b), and find the sum to calculate delta H.