Which of these scenarios involve a reaction that is at equilibrium?
a. the reaction is producing reactants and products at an equal rate.
b. the reaction is producing more reactants than products.
c. the reaction is only producing products
d. the reaction is producing more products than reactants.

a. the reaction is producing reactants and products at an equal rate. is the  correct answer.

Explanation:

If a reaction is at equilibrium then the reaction rates for both the reverse and forward directions are equal.

catalyst that increases the reaction rate of a  reaction, but it does not change the equilibrium state for that reaction.

Thus at the equilibrium stage, the concentration of the reactants and the product remain constant.

given:

mass of na = 115 g

excess cl2

to determine:

mass of nacl produced

explanation:

given reaction is-

2na(s) + cl2(g) → 2nacl(s)

since cl2 is in excess, na will be the limiting reagent

as per the reaction stoichiometry na: nacl = 1: 1

i.e. moles of na reacted = moles of nacl formed

now, # moles of na = mass of na/atomic mass

                                  = 115 g/23 g.mol-1 = 5 moles

therefore, moles of nacl = 5

molar mass of nacl = 58 g/mol

mass of nacl = 5 moles * 58 g.mol-1 = 290 g

ans: amount of nacl produced = 290 g

answer : a model is often used to explain and make things easier to understand when any scientific topic needs to be demonstrated and explained.

as in this case where a scientist wants to use a model to present the results of his detailed scientific investigation. he should do it as it will him to make the audience understand the concept in a much better way. also, it can be changed according to new scientific understandings.