Chapter 6, Problem 6.30QP

Enthalpy

1. a A 100.-g sample of water is placed in an insulated container and allowed to come to room temperature at 21°C. To heat the water sample to 41°C, how much heat must you add to it?
2. b Consider the hypothetical reaction, $2\text{X}(aq)+\text{Y}(l)\to {\text{X}}_2\text{Y}(aq)$being run in an insulated container that contains 100. g of solution. If the temperature of the solution changes from 21°C to 31°C, how much heat does the chemical reaction produce? How does this answer compare with that in part a? (You can assume that this solution is so dilute that it has the same heat capacity as pure water.)
3. c If you wanted the temperature of 100. g of this solution to increase from 21°C to 51°C, how much heat would you have to add to it? (Try to answer this question without using a formula.)
4. d If you had added 0.02 mol of X and 0.01 mol of Y to form the solution in part b, how many moles of X and Y would you need to bring about the temperature change described in part c.
5. e Judging on the basis of your answers so far, what is the enthalpy of the reaction 2X(aq) + Y(l)→ X₂Y(aq)?