I did an experiment to determine enthalpy change when Zinc is added to Copper(II) sulphate solution.
I recorded values and plotted a temperature-time graph to obtain values of the temperature change to calculate heat transfer .
The trend line that I obtained is when temperature of the mixture started to drop.
I never knew why I needed to extend that trend line and draw a vertical line at the point when Zinc is added and thus never understood why the difference between the interception point and the point when Zinc is added is $\Delta T$
To summarise, I don’t understand why I need to extend the trend line and the interception point gives the highest ‘T’ value...