Thermochemistry

[tylerngo]

When 10.00 mL of a solution of strong acid is mixed with 100.00 mL of a solution of weak base in a coffee-cup calorimeter, the temperature rises from 22.0 oC to 26.7 oC. Determine q for the acid-base reaction, assuming that the liquids have densities of 1.00 g/mL and the same heat capacities as pure water.

So I tried adding the solutions and then using the equation q=mc deltaT to be the q value but I was told I was getting the wrong answer and was unable to find the correct answer anywhere after contacting friends.

If you can tell me where i got the answer wrong please let me know.

 

Brumer

[Mumbles]

The biggest issue is using the incorrect heat capacity © in terms of units. Water has a heat capacity of 1 cal/g*deg K, or 4.184 to 4.1868 joule/g*deg K for water depending on which constant you use. Delta T is the same in both Kelvin or celcius. Your heat of reaction should be:

 

q = (110g)*c(in correct units)*(4.7 deg)

 

I got 517 calories or 2164.1-2164.6 joules. The joule value will vary a few fractions of a J depending on which constant you use. Things get a bit more complicated to calculate if you have to take into account the heat capacity of the calorimeter or take into account the varying heat capacity of water with temperature, which is probably only a factor is fairly advanced physical chemistry lab examples. The number of significant figures in the joules heat capacity sometimes matters if you're entering into a computer system.