Calculate the mass of ethanol that must be burnt to increase the temperature of 150g of water by 75 degrees celsius, if exactly 75% of the heat released by this combustion is lost to the surroundings. Also it is given that the heat of combustion of ethanol 1367 kJ.mol^-1 and the specific heat capacity of water is 4.18x10^3 J.kg^-1.K^-1.
what are two ways to limit heat loss from this experiment ?
How much heat do you need?
q = mass H2O x specific heat H2O x dT
q = 150g x 4.18 J/g x 75 = approx 47000 J but you need to go through all of these calculations and redo them for better accuracy.
You will lose 75% (or keep 25%) so we must increase that to approx 47,000/0.25 = approx 188,000. (Check that out to make sure it's right. If we have 188,000 and lose 75% we lose 188,000 x 0.75 = 141,000. That leaves us with 188,000-141,000 = 47,000 J that we can use.)
C2H5OH + 3O2 --> 2CO2 + 3H2O + 1367 kJ/mol.
1367 kJ/mol x #mol = 188 kJ
Solve for #mol and convert mols to grams ethanol. g = mols x molar mass.
To calculate the mass of ethanol that must be burnt, we can use the following steps:
Step 1: Calculate the energy required to heat the water:
The energy required to heat 150g of water by 75 degrees Celsius can be calculated using the formula:
Q = mcΔT
where:
Q is the energy in Joules (J)
m is the mass of water in kg (150g = 0.15kg)
c is the specific heat capacity of water in J.kg^-1.K^-1 (4.18x10^3 J.kg^-1.K^-1)
ΔT is the change in temperature in Kelvin (75 degrees Celsius = 75 + 273.15 = 348.15K)
Using the formula, we get:
Q = (0.15kg)(4.18x10^3 J.kg^-1.K^-1)(348.15K)
Step 2: Calculate the total energy released by the combustion reaction:
The energy released by burning ethanol can be calculated using the heat of combustion, which is 1367 kJ.mol^-1. We need to convert it from kilojoules to joules by multiplying by 1000:
Energy released by 1 mole of ethanol = 1367 kJ/mol x 1000 J/kJ
Step 3: Calculate the energy lost to the surroundings:
Given that 75% of the heat released by the combustion is lost, we need to calculate the remaining 25%:
Energy lost = (25/100) x Energy released
Step 4: Calculate the number of moles of ethanol burnt:
To find the number of moles of ethanol, we need to divide the energy lost by the energy released by 1 mole of ethanol:
Number of moles = Energy lost / Energy released per mole
Step 5: Calculate the mass of ethanol used:
To calculate the mass of ethanol, we need to multiply the number of moles by the molar mass of ethanol, which is 46.07 g/mol.
Now that we know how to calculate the mass of ethanol, let's move on to discussing two ways to limit heat loss from this experiment:
1. Insulation: One way to limit heat loss is to insulate the system. This can be done by using a well-insulated container to hold the water, such as a double-walled flask or a calorimeter. The container should have low thermal conductivity to minimize heat transfer to the surroundings.
2. Stirring: Another way to limit heat loss is by stirring the water during the experiment. By continuously stirring the water, the heat is distributed more evenly within the liquid, reducing temperature gradients and minimizing heat loss to the surroundings.
By implementing these measures, the heat loss can be minimized, leading to more accurate calculations and results in the experiment.