thermochemistry and hess\'s law a. When solutions of two reactants were mixed in

Question

thermochemistry and hess's law

a. When solutions of two reactants were mixed in a coffee-cup cal hen solutions of two reactants were mixed in a coffee-cup calorimeter, the following temperatures were recorded as a function of time. Plot the data on one of the available pieces of graph paper. Obtain ts the final temperature, by extrapolating to the time of mixing (time - 0 s) with a straight line through the data to the point where it intersects the y-axis of your graph. The initial temperature, ti, was 24.3°C. Time (s) t (C) 40.5 40.4 40.3 40.2 Time (s) t (°C) 30 60 90 120 40.4 40.8 40.7 40.6 150 180 210 240 ty:

Explanation / Answer

In a plot T(temperature) vs. t(time) read Tf at t=0.

Tf = 41.0 oC

Tf can be observed only in the hypothetical case when the reaction and the heat transfer to solution are instant (t=0) without losses to environment (what we see after t= 60 s).

In the first 60 sec we have heating, but also heat loss: this is the reason we have to extrapolate data to obtain the value of the maximum temperature.

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