A flask runs the reaction 2 A → 3 B. Slide the time marker along the curve. The tangent gives the rate at that instant, and the dotted line gives an average over a stretch.
Concentration against time teal falls, gold climbs
What is in the flask right now per liter
t = 0 sNothing has reacted yet. This is where the initial rate is measured.
Loss of A, this instant
0.0300 M/s
Rate of reaction
0.0150 M/s
Gain of B, this instant
0.0450 M/s
Average loss of A
0.0094 M/s
[A] now
0.600 M
[B] now
0.000 M
Half-life of A
13.9 s
Fraction of A left
100 percent
Speed
Set up the run
What to notice
The slope is steepest at the start
Drag the marker to the right. The tangent flattens as you go, because A is running out. The average over a window always lands between the two instant rates at its ends.