Which of the following best defines the instantaneous rate of a chemical reaction at a particular moment in time?
a) The slope of a straight line connecting that point on the curve to the origin
b) The average rate calculated over a short but finite time interval immediately following that moment
c) The slope of a tangent drawn to a concentration–versus–time curve at that moment
d) The slope of a tangent drawn to a rate–versus–time curve at that moment