intro chem HELp please
posted by John .
1. Zinc is often used to calibrate calorimeters because it undergoes a very sharp phase transition from the solid to the liquid at 419.5oC. Calculate the enthalpy change when 5 g of zinc metal is heated from 100oC to the point where the entire sample is melted. (The heat of fusion for zinc is 112.4 J/g and its specific heat capacity is 0.388 J/goC.)
2. A 235 gram block of iron is heated to 450 °C and then is dropped into a coffee cup calorimeter containing 250 g of water at 25.0 °C. What is the final temperature of the system to the nearest 0.1 °C? (Assume all heat is transferred to the water)
Specific heat capacity of iron = 0.451 J/(g*°C)
Specific heat capacity of water = 4.18 J/(g*°C)
q1 for Zn to move from 100 C to 419.5 C.
q1 = mass Zn x specific heat x (Tfinal-Tinitial).
q2 = heat to melt Zn
q2 = mass Zn x delta Hfusion.
Total heat = q1 + q2
For the iron,
heat lost by iron + heat gained by water = 0.
[mass Fe x specific heat Fe x (Tfinal-Tinitial)] + [mass water x specific heat water x (Tfinal-Tinitial)] = 0
Solve for Tfinal.