A 2.75 g sample of the hydrocarbon acetone, CH3COCH3, is burned in a bomb calorimeter with 975 mL of water, initially at 23.50 degrees celsius. The bomb is constructed of 285.0 g of nickel metal having a specific heat capacity of Cp = 0.826 J/ g degrees C. The final temperature of the bomb and the water after the combustion process increases to 29.55 degrees celsius. calculate the following:
(a)The heat flow at constant volume, qv for this combustion (in kJ/mol).
i know qv = delta E. and that delta E = q + w. but how do i find the work? i know work = force / distance. (i'm struggling because my book gives an example where the work is already given so it is not helpful at all.)
(b)The energy released per mole of acetone (in kj/mole).
(c)calculation (b) amounts to the heat of combustion per mole, delta h comb/mole for this compound. Balance the reaction for the complete combustion of acetone, find delta n and then find the value of delta H per mole of acetone (kJ/mole).
i don't know how to even start part (b).
To solve this problem, let's break it down into steps:
(a) Finding the heat flow at constant volume, qv:
To find qv, we need to calculate the change in internal energy (delta E). As you correctly mentioned, delta E = q + w, where q is the heat absorbed or released, and w is the work done.
In this case, since the reaction is done in a bomb calorimeter at constant volume, no work is done (w = 0). So we have:
delta E = q
Now, to find q, we can use the equation:
q = m * Cp * delta T
where m is the mass of the water, Cp is the specific heat capacity of the water, and delta T is the change in temperature.
Given:
m_water = 975 g
Cp_water = 4.186 J/g°C
delta T = (final temperature - initial temperature) = (29.55°C - 23.50°C)
Now, calculate q.
(b) Finding the energy released per mole of acetone:
To find the energy released per mole of acetone, we need to know the number of moles of acetone in the sample.
Given the molar mass of acetone is 58.08 g/mol and the mass of the acetone sample is 2.75 g, we can calculate the number of moles using the equation:
moles = mass / molar mass
Now, divide q (from part a) by the number of moles of acetone to get the energy released per mole.
(c) Finding the heat of combustion per mole, delta H comb/mole:
To find the heat of combustion per mole, we need to balance the combustion reaction of acetone and use the stoichiometric coefficients to determine the number of moles of acetone consumed and the change in enthalpy (delta H) for the reaction.
The balanced equation for the combustion of acetone is:
2 C3H6O + 9 O2 → 6 CO2 + 6 H2O
From the balanced equation, we can see that for every 2 moles of acetone, 6 moles of CO2 are produced.
Now, determine the number of moles of acetone consumed in the reaction based on the number of moles of CO2 produced.
Finally, divide the energy released per mole (from part b) by the number of moles of acetone consumed to get the heat of combustion per mole (delta H comb/mole).