Substance Heat of Fusion Heat of Vaporization H2O 6.01...

Substance Heat of Fusion Heat of Vaporization H2O 6.01 kJ/mol 40.7 kJ/mol Benzene (C6H6) 10.59 kJ/mol 30.8 kJ/mol Ethanol (C2H5OH) 4.60 kJ/mol 43.5 kJ/mol Acetone (CH3COCH3) 5.72 kJ/mol 29.1 kJ/mol How much heat is released when 85.3 g of ethanol changes from a gas to a liquid at its condensation point? (hint: heat is being released so use the negative heat of fusion or heat of vaporization) - 392 kJ - 8.51 kJ - 3710 kJ - 80.5 kJ

Transcript

00:01 A typical heating and cooling curve, such as that of ethanol, might look something like this, where you have temperature plotted on the y -axis versus energy or energy transfer in the form of heat on the x -axis.

00:12 And when you get to the freezing melting point, it's isothermal.

00:16 It goes flat.

00:16 There's no temperature change.

00:18 And then it might rise again in the liquid phase, go through an isothermal point, and the vaporization phase change, and then begin to increase again.

00:28 Now, there are three points of this curve that have a slope, right? so this is when the material is in the solid phase, this is when it's in the liquid phase, and this is when it's in the gas phase.

00:42 And all three of the energy changes during those points can be calculated with q equals m -c -delta -t, delta -t being the temperature change, c being the specific heat of the material, and m being the mass.

00:57 However, along the flat parts of the curve, we have a different formula.

01:06 So in the change from liquid to gas, going in that direction, we call it vaporization, going in the other direction from gas to liquid, we call it condensation.

01:17 But during this phase, the energy is used to break intermolecular forces and not really change the kinetic energy of particles.

01:25 So we use a little different formula since there's no, temperature change during a phase change.

01:31 We use the mass of the material times the heat of vaporization here, symbolized hv.

01:40 And between the solid and the liquid, if we're going to solid liquid, that direction, we know that is called melting, going from liquid to solid is freezing.

01:50 And during that phase change, we would calculate the energy.

01:53 You need to go through that phase change by taking the mass times hf, the heat of fusion.

02:00 So notice there's no delta t or temperature change during that time.

02:04 Now, let's assume we have a sample of ethanol that is 85 .3 grams of ethanol...

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