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TheChiScientist wrote:Straight outta AP Chem. (Question is aimed at Div. C. Sorry Div. B!)
When a student mixes 50 mL of 1.0 M HCl and 50 mL of 1.0 M NaOH in a coffee-cup calorimeter, the temperature of the resultant solution increases from 21.0 °C to 27.5 °C. Calculate the enthalpy change for the reaction in kJ per mol of HCl, assuming that the calorimeter loses only a negligible quantity of heat. The total volume of the solution is 100 mL, its density is 1.0 g/mL, and its specific heat is 4.18 J/g-K.

 



(Since we're considering a range, actually converting the temperatures to Kelvin would yield the same answer.)







Technically, the final answer should have one significant figure, but...

UTF-8 U+6211 U+662F wrote:

TheChiScientist wrote:Straight outta AP Chem. (Question is aimed at Div. C. Sorry Div. B!)
When a student mixes 50 mL of 1.0 M HCl and 50 mL of 1.0 M NaOH in a coffee-cup calorimeter, the temperature of the resultant solution increases from 21.0 °C to 27.5 °C. Calculate the enthalpy change for the reaction in kJ per mol of HCl, assuming that the calorimeter loses only a negligible quantity of heat. The total volume of the solution is 100 mL, its density is 1.0 g/mL, and its specific heat is 4.18 J/g-K.

Click to Show Answer

 



(Since we're considering a range, actually converting the temperatures to Kelvin would yield the same answer.)







Technically, the final answer should have one significant figure, but...

Side note: I wish the built-in renderer included the SI package...

UTF-8 U+6211 U+662F wrote:A gas is allowed to freely expand to a box which is five times the volume the previous container was. What is the resulting entropy change? A gas expands reversibly until its volume is five times as much. What is the resulting entropy change? Explain the difference between free expansion and reversible expansion.

MattChina wrote:

UTF-8 U+6211 U+662F wrote:A gas is allowed to freely expand to a box which is five times the volume the previous container was. What is the resulting entropy change? A gas expands reversibly until its volume is five times as much. What is the resulting entropy change? Explain the difference between free expansion and reversible expansion.

5 times, 0, free expansion is irreversible and the entropy change is greater than zero, while reversible expansion has no entropy change.

1) Increases by [math]Nk_B\ln 5[/math] or equivalently [math]nR\ln 5[/math], where N is the number of particles, k is the Boltzmann constant, n is the number of moles, and R is the ideal gas constant
2) Yep! Just note that only the net entropy change (of both the gas and the surroundings) is 0. The entropy of the gas itself can increase or decrease.
3) Yep!

UTF-8 U+6211 U+662F wrote:What were Clausius's and Kelvin's formulations of the Second Law of Thermodynamics?

Crimesolver wrote:

UTF-8 U+6211 U+662F wrote:What were Clausius's and Kelvin's formulations of the Second Law of Thermodynamics?

Clausius's formulation was "it is impossible for a self-acting, unaided by any external agency, to trader heat from a body at lower temperature to a body, at a high temperature.
Kelvin's formulation was "it is impossible to obtain a continuous supply of energy by cooling a body below the coldest of it's surroundings."