5. Which happens when a reversible reaction reaches a state of chemical equilibrium?
The system runs out of reactant particles.
The activation-energy barrier is eliminated.
The concentrations of reactants and products are equal.
The rates of forward and reverse reactions are equal.

since the atomic number is the number of protons in the nucleus, as we move to the left on the periodic table, the electrostatic pull between the nucleus and the valence electron shell decreases. as we move down a group (vertical column), the valence shell energy level gets further and further from the nucleus.

the answer is   c.) 1575 j.

explanation: