Pure Competition: Profit Maximizing in Long Run

Long-run competitive equilibrium:
is realized only in constant-cost industries.
We would expect an industry to expand if firms in that industry are:
Earning economic profits.
When a purely competitive firm is in long-run equilibrium:
Price equals marginal cost.
A purely competitive firm is precluded from making economic profit in the long run because:
Of unimpeded entry to the industry.