### Significant Figures

Posted:

**Wed Feb 01, 2017 5:56 pm**Hi. This question is for TA Jack, who read my email and said he would answer this:

When we use bond enthalpy, reactant - product, and Hess's Law, assuming that we have exact numbers of moles (from the equation), the significant figures in the answer are ONLY limited by addition, right?

For instance: 25 kJ/mol (2 mol) - 3274 kJ/mol * 1 mol = -3224 kJ

There is no rounding to two significant figures (the 25kJ/mol does NOT limit the answer to 2 sig fig). It stays at 4 because every number is significant *until the ones digit*, right? The way I see this is that it is 50. KJ - 3274 kJ, because I think that the multiplication does not affect significant figures.

Thank you.

When we use bond enthalpy, reactant - product, and Hess's Law, assuming that we have exact numbers of moles (from the equation), the significant figures in the answer are ONLY limited by addition, right?

For instance: 25 kJ/mol (2 mol) - 3274 kJ/mol * 1 mol = -3224 kJ

There is no rounding to two significant figures (the 25kJ/mol does NOT limit the answer to 2 sig fig). It stays at 4 because every number is significant *until the ones digit*, right? The way I see this is that it is 50. KJ - 3274 kJ, because I think that the multiplication does not affect significant figures.

Thank you.