calorimetry / thermodynamics problem

Question

1 a. Assume that it is possible to heat water with perfect insulation (all the heat from combustion of ethanol is transferred to water).

How much energy (in joules) is needed to heat 200.0 g of water by 10.0°C? The heat capacity of water is 4.184 J/g · °C

energy:

b. How many millimoles of ethanol would need to be burned to generate the amount of energy that is needed to heat 200.0 g of water by 10.0°C The heat of combustion of ethanol is –1368 kJ/mol. 

millimoles of ethanol:

c. What is the volume of ethanol required to heat 200.0 g of water by 10°C?The density of ethanol is 0.78 g/mL.

volume:

Answer 1

(a) q = mC∆T where q = heat = ?; m = mass of water = 200.0 g; C = sp.heat = 4.184 J/gº; ∆T = change in temperature = 10.0º

q = (200.0 g)(4.184 J/gº)(10) = 8368 J

(b) Combustion of ethanol: C2H5OH + 3O2 ==> 2CO2 + 3H2O ... balanced equation

mol C2H5OH needed to generate 8368:

8368 J x 1 kJ/1000 J x 1 mol C2H5OH / 1368 kJ = 0.006117 moles

millimoles ethanol = 6.12 millimoles

(c) 0.006117 moles ethanol x 46.07 g/mol = 0.2818 g ethanol

0.2818 g x 1 ml/0.78 g = 0.361 ml