Three groups of drugs are used to reduce the stickiness of platelets, thus preventing platelets from clumping together to form platelet plugs. The anti-platelet drugs are most effective in preventing abnormal blood clots from forming in arteries (as opposed to veins). Aspirin and dipyridamoleâ (Aggrenox).
In order to react, colliding molecules must have a total kinetic energy equal to or greater than some minimum value [Figure 14.13(b)]. The minimum energy required to initiate a chemical reaction is called the activation energy, Ea. The value of Ea varies from reaction to reaction.
The activation energy [Activation energy: The minimum energy required for a collision between particles, in order for a reaction to occur.] (E a) for the forward reaction is shown by (A): E a (forward) = H (activated complex) - H (reactants) = 200 - 150 = 50 kJ mol-1. The activation energy (E a) for the reverse reaction is shown by (B): E a (reverse) = H (activated complex) - H (products) = 200 - 50 = 150 kJ mol-1. The enthalpy change for the forward reaction is shown by (C):