MHS Chemistry
An Endothermic Chemical Reaction

In this lab, you will be investigating heat in a chemical reaction. Perform each of the following steps in order, filling in the blanks as you go. Show your work in the spaces provided.

The formula for ammonium thiocyanate is NH4SCN
The formula for barium hydroxide octahydrate is _______________.

These two chemicals react to form ammonia (formula NH3 ), water, and barium thiocyanate (formula Ba(SCN)2 ). Write the balanced chemical equation for this reaction:



Carefully measure the indicated amounts of each reactant into separate containers. Note that barium hydroxide contains a heavy metal, and should be treated gently and carefully at all times. Determine the molecular weight and number of moles of each.

ammonium thiocyanate MW = __________ g/mol
3.000 g =

_______________ moles


barium hydroxide octahydrate MW = __________ g/mol
6.000 g =
_______________ moles

Based on your balanced equation and the amounts above, which chemical, if any, is going to be a limiting reactant?


Determine the number of moles of water that should be formed by mixing these two chemicals.



Determine the number of grams of water that should be formed by mixing these two chemicals.



Assume the chemicals start out at room temperature. This is _______________ °C.

Mix the two chemicals in a small beaker. Gently stir the mixture around with the thermometer. Notice any changes that take place.

Keep track of the temperature after you mix the chemicals. Take note of the extreme temperature reached. The [highest, lowest] temperature reached by the mixture after combination was _______________ °C.

Since the water [gained, lost] energy, the reaction must have [gained, lost] energy. This means that the reaction is [endothermic, exothermic, miskatonic, umathermic].

Recall from earlier in the year how to calculate a heat change from a temperature change. Complete the equation:

q = _______________

Calculate the heat change (including sign) of the water in this reaction. Assume ("pretend") that the water produced acts like pure water. Remember that water has a density of 1.0 g/mL, and the specific heat of water is 1 cal/gC°.

                  q(water) = _______________ calories

therefore, q(reaction) = _______________ calories

Calculate the heat change per mole of barium hydroxide reacted.

                  q(reaction) = _______________ cal/mol barium hydroxide

Write down the balanced equation from the other side of this sheet again, but this time include the appropriate amount of energy as a product or reactant.

DISPOSAL The solution produced should be poured into the waste beaker provided. The test tube should be rinsed into the same beaker, then placed in the dishwasher.

[MHS Chemistry Page]