2CH3OH(l)+3O2(g)-->2CO2(g)+4H20 +1350 kj
1. What mass of water could be heated from 20.0 C to 35 C,by burning 48g of methanol?
This is what I did, no answer was given so I want to double check.
so q=mcT change in H=n(molar enthalpy)
c= 4.184 kj/(kg C)
So what I did was divide 1350 kj by 2 to get the molar enthalphy of methanol.
Than from the mass given I found the mols of methanol; about 1.5 mols. I than multipled 1.5 mols by 675 kj/mol. I found the enthalpy to be 1013 kj. Than using the quanity of heat equation Q=mcT I found the mass of water to be 16 kg.
I worked it separately and obtained 16.1 kg. I don't know how many zeros you have on 35 degrees and 48 g so watch the significant figures. You appear to have used the correct procedure.
To find the mass of water that could be heated from 20.0°C to 35°C by burning 48g of methanol, you can follow these steps:
1. First, calculate the molar enthalpy of methanol (CH3OH) using the given information. The balanced equation for the combustion of methanol shows that 2 moles of methanol produce 1350 kJ of heat. Therefore, the molar enthalpy of methanol is 1350 kJ / 2 moles = 675 kJ/mol.
2. Next, determine the number of moles of methanol that are being burned. You are given that the mass of methanol is 48g. To convert this mass to moles, divide by the molar mass of methanol. The molar mass of methanol is 32.04 g/mol (1 carbon atom + 4 hydrogen atoms + 1 oxygen atom). So, 48 g / 32.04 g/mol ≈ 1.498 moles.
3. Now, calculate the heat released by burning this amount of methanol. Multiply the number of moles of methanol by the molar enthalpy: 1.498 moles × 675 kJ/mol ≈ 1012.65 kJ (rounded to three significant figures).
4. Finally, use the heat equation q = mcΔT to calculate the mass of water that can be heated. The values for specific heat capacity (c) and temperature change (ΔT) are given. The specific heat capacity of water is approximately 4.184 J/g°C, which is equivalent to 4.184 kJ/kg°C.
To apply the heat equation, convert the given temperatures to Kelvin by adding 273.15 to each value. The initial temperature (20°C) becomes 20 + 273.15 = 293.15 K, and the final temperature (35°C) becomes 35 + 273.15 = 308.15 K.
Substituting the values into the heat equation:
q = mcΔT
1012.65 kJ = m * 4.184 kJ/kg°C * (308.15 K - 293.15 K)
Rearranging the equation to solve for the mass (m):
m = 1012.65 kJ / (4.184 kJ/kg°C * (308.15 K - 293.15 K))
Evaluating the expression:
m ≈ 15.991 kg
Therefore, the mass of water that could be heated from 20.0°C to 35°C by burning 48g of methanol is approximately 15.991 kg, which can be rounded to 16 kg.