# How do I build a thermochromic thermometer?

My Chem 152 lab is requiring us to build a thermochromic thermometer utilizing methods from previous labs such as absorbance spec and temp.

We've been taught how to calculate Kc values successfully as well as delta H and delta S from these methods, but I'm unsure of how to combine everything into creating a thermochromic thermometer.

We're given $\ce{CoCl2(EtOH)2}$ and $\ce{CoCl2(iPrOH)2}$ to react with $\ce{MeOH}$. We had to complete a pre-lab assignment by calculating $K_c$ values at $275\ \mathrm{K}$ using $\Delta H$ and $\Delta S$ values from a reaction of $\ce{CoCl2(EtOH)2/MeOH}$ and a reaction of $\ce{CoCl2(iPrOH)2/MeOH}$. I was able to determine whether each reaction was reactant or product favored based on their $K_c$ values, but I'm completely stumped on how to use all of this information in creating a thermochromic thermometer.

We calculate the $K_c$ values. Ratios that give $K_c$ greater than 1 are product favored and will turn from blue to pink at low temps. The opposite is true for the ratios that give $K_c$ values less than 1. These are reactant favored, and will turn from pink to blue at the low temp. First, look to see what is chaging color most drastically, meaning the reaction is proceding to a greater extent ($K_c$ value a lot greater than or less than 1), then look at the cost. If it's too expensive, a thermometer that is less effective but still OK, may be better.