What is the term used for a well insulated reaction vessel used to measure delta H of reactions?

Often the determination of the enthalpy of reaction can be done in a coffee-cup calorimeter, otherwise known as a constant-pressure calorimeter.

This device is often well-insulated so that we can rightfully say,

#q_(soln) ~~ -q_(rxn)#

That is, #q_(soln)# and #q_(rxn)# are opposite in sign!

At constant pressure, the heat flow through the solution, #q_(soln)# is equal to the enthalpy of solution, #DeltaH_"soln"# in units of #"J"#.

This heat flow came out into the solution due to the reaction, so by conservation of energy, #q_(soln) = -q_(rxn)#. We thus have in, #ul"J/mol"#, that

#color(blue)(q_(soln)/(n_("product")) = -DeltabarH_(rxn))#,

for the relationship through which one can find the enthalpy of a reaction that occurs in a solution inside the coffee-cup calorimeter, where #n_("product")# is the mols of the reaction product.

For the solution heat flow, we write:

#q_(soln) = m_(soln)C_(soln)DeltaT#,

and we often approximate the solution heat capacity #C_(soln)# as the heat capacity of water, i.e. #C_(soln) ~~ "4.184 J/g"^@ "C"#.

The mass of the solution, #m_(soln)#, is generally approximated by knowing its volume (by measurement!) and assuming the density of the solution is that of water, #"1 g/mL"#.

Thus, by measuring the temperature change in the solution, and knowing how much solution was measured out, one can determine #q_(soln)# and consequently determine #DeltaH_"rxn"#.