Answer:
In science, amodel is a representation of an idea, an object or even a process or a system that is used to describe and explain phenomena that cannot be experienced directly. Models are central to what scientists do, both in their research as well as when communicating their explanations.
Explanation:
I believe the correct answer from the choices listed above is option D. Catalysts lower the activation energy of a chemical reaction. It <span>is a substance which speeds up a reaction, but is chemically unchanged at the end of the reaction. It provides another pathway for the reaction to occur.</span>
Actually, the ionic equation for this is a reversible
equation since codeine is a weak base. Any weak base or weak acids do not
completely dissociate which makes them a reversible process. The ionic equation
for this case is:
<span>C18H21O3N + H3O+ </span><=>
C18H21O3NH+ + H2O
We know that to relate solutions of with the factors of molarity and volume, we can use the equation:

**
NOTE: The volume as indicated in this question is defined in L, not mL, so that conversion must be made. However it is 1000 mL = 1 L.
So now we can assign values to these variables. Let us say that the 18 M

is the left side of the equation. Then we have:

We can then solve for

:

and

or

We now know that the total amount of volume of the 4.35 M solution will be
210 mL. This is assuming that the entirety of the 50 mL of 18 M is used and the rest (160 mL) of water is then added.