Question

what can 1) increase the probability that reactants encounter each other in the correct spatial orientation for the reaction to occur, and 2) lower activation energies?
the answer is one word: enzymes.
enzymes are proteins that act as catalysts, meaning that they make reactions go faster but arent changed by them - the structure of an enzyme is the same before and after the reaction. more specifically, proteins have areas called active sites where a particular chemical reaction takes place.
each enzyme catalyzes one particular reaction because the size, shape, and chemical composition of the active site is such that the reactants fit into the space, bind to r - groups in the active site in a way that places them 1) in the correct orientation to each other, and 2) in close proximity to charges or protons or other components of r - groups that stabilize the transition state and lower the reactions activation energy.
the active site is where reactants encounter each other in the correct spatial orientation, and where bonds that are being broken are stabilized by interactions with specific r - groups, so the activation energy threshold goes down.
one more key point about enzymes: they dont change the free energy of the reactants or the products, meaning that they dont make nonspontaneous reactions spontaneous or vice versa. they just make it much more likely that a spontaneous reaction will actually occur.
why is it appropriate to call an active site \active?\ select the single best answer.
○ its the place where a nonspontaneous reaction becomes an active, spontaneous one.
○ because of its size, shape, and chemical activity, the site is specific to one particular reaction.
○ its the location where chemical activity—a reaction—takes place.
enzymes make nonspontaneous reactions go.

Explanation:

The text states that the active site is where a particular chemical reaction takes place. The first option is incorrect as enzymes don't make non - spontaneous reactions spontaneous. The second option is about the specificity of the active site (size, shape, chemical activity) but doesn't really explain why it's called "active". The third option directly relates to the fact that it's the location of chemical activity (a reaction).

Answer:

It's the location where chemical activity—a reaction—takes place.