Question

A student sets up the following equation to convert a measurement.

Answer 1

Answer:

$\frac{1 kJ}{1,000 J}$  ·  $\frac{1,000 mmol}{1 mol}$

Explanation:

The final answer has a different set of units. In particular, millimoles (mmol) changes to moles (mol) and joules (J) changes to kilojoules (kJ). To make this change, you need to multiply the first value by proportions.

When writing these proportions, it is important that they are arranged in a way that allows for the cancellation of units. For instance, since J is located in the numerator, it must be located in the denominator of the conversion. Furthermore, since mmol is located in the denominator, it must be located in the numerator of the conversion.

Proportions:

1,000 J = 1 kJ

1,000 mmol = 1 mol

The full expression:

$-1.3*10^4\frac{J}{mmol*^oC}$  ·  $\frac{1 kJ}{1,000 J}$  ·  $\frac{1,000 mmol}{1 mol}$  =  $? \frac{kJ}{mol*^oC}$
                        ^           ^

As you can see, the old units cancel out and you are left with kJ in the numerator and mol in the denominator.