1) The specific heat of solid copper is 0.385 J/g(C). What thermal energy change occurs when the temperature of a 34.10 g sample of copper is cooled from 35.7 degrees Celsius to 13.9 degrees Celsius?
Answer: -286.3 J
This amount of heat is used to melt solid ice at 0.0 degrees Celsius. The molar heat of fusion of ice is 6.00 kJ/mol. How many moles of ice are melted?
Answer: ???
2) Brazilians are quite familiar with fueling their automobiles with ethanol, a fermentation product from sugarcane. Calculate the standard molar enthalpy for the complete combustion of liquid ethanol (C2H5OH) using the standard enthalpies of formation of the reactants and products.
C2H5OH(l) + 3O2(g) --> 2CO2(g) + 3H2O(g)
a)
q = mass x specific heat x (Tfinal-Tinitial)
b)
Write the equation and balance it.
deltaHfrxn = (n*DHfproducts)-(n*DHfreactants)
You can find the delta Hf products and reactants in your text or notes.
nya
56.3
To calculate the number of moles of ice melted using the given molar heat of fusion, we can use the following steps:
1. Determine the amount of thermal energy change using the specific heat formula:
q = m * c * ΔT
where:
q = thermal energy change
m = mass of the sample (34.10 g)
c = specific heat of copper (0.385 J/g°C)
ΔT = change in temperature (-21.8°C, calculated as 13.9°C - 35.7°C)
Plugging in the values:
q = 34.10 g * 0.385 J/g°C * (-21.8°C)
q ≈ -286.3 J (rounded to one decimal place)
2. To find the number of moles of ice melted, we need to convert the thermal energy change from joules to kilojoules, and then divide it by the molar heat of fusion:
-286.3 J ÷ 1000 = -0.2863 kJ (convert from joules to kilojoules)
Now, we can use the molar heat of fusion to find the moles of ice:
-0.2863 kJ ÷ (-6.00 kJ/mol) = 0.0477 moles (rounded to four decimal places)
Therefore, approximately 0.0477 moles of ice are melted.
For the second question, to calculate the standard molar enthalpy for the complete combustion of liquid ethanol (C2H5OH), we need to use the standard enthalpies of formation for the reactants and products involved.
The standard enthalpy of formation is the change in enthalpy that occurs when one mole of a compound is formed from its elements in their standard states.
Using the standard enthalpies of formation, we can calculate the standard molar enthalpy by applying Hess's Law, which states that the sum of the enthalpy changes for a series of reactions is equal to the overall enthalpy change.
To calculate the standard molar enthalpy for the combustion of liquid ethanol, we can subtract the standard enthalpies of formation of the reactants from the standard enthalpies of formation of the products, multiplied by their stoichiometric coefficients:
ΔH° = (2*ΔHf°(CO2) + 3*ΔHf°(H2O)) - (ΔHf°(C2H5OH) + 3*ΔHf°(O2))
where:
ΔH° = standard molar enthalpy
ΔHf° = standard enthalpy of formation
Substituting the values for the standard enthalpies of formation, we can calculate ΔH°.