Chemsitry Question

Question

A 2‎‎5.0-g samp‎‎le of etha‎‎nol (C₂‎‎H₅OH) at 25.0 °C is hea‎‎ted by the ‎‎additi‎‎on of 40‎‎0.0 J of e‎‎nergy. What is the fi‎‎nal tempe‎‎rature of et‎‎hanol? The spe‎‎cific heat ca‎‎pacity of liqu‎‎id ethanol is 2‎‎.46 J/g‎‎·K.

Select one:

a.

56.3 °C

b.

55.7 °C

c.

31.5 °C

d.

6.50 °C

Answer 1

The equation we want to use is q = mC∆T

q = heat = 400.0 J (4 sig. figs.)

m = mass = 25.0 g (3 sig. figs.)

C = specific heat = 2.46 J/gº (3 sig. figs.)

∆T = change in temperature = ?

Solving for ∆T, we have...

∆T = q / mC = 400.0 J / (25.0 g)(2.46 J/gº)

∆T = 6.50º

Final temperature = 25.0º + 6.50º = 31.5ºC (Answer c)

NOTES:

Since heat is ADDED to the sample, we add the ∆T to the initial temperature.

Even though C is given in J/g-K, since we are looking at ∆T (a change in temperature), the scale doesn't matter since a 1º change in Celsius is the same as a 1º change in K. You can just as easily use C = 2.46 J/gºC, it's the same thing).