What is the difference between an open system and a closed system

Which element in the third period would you expect to have the larger atomic radius, sodium (na) or sulfur (s)? a. sodium, because it has a higher effective nuclear charge attracting electrons in fewer energy levels. b. sodium, because it has fewer protons attracting electrons in the same energy levels. c. sulfur, because it has more protons attracting electrons in more energy levels. d. sulfur, because it has a higher effective nuclear charge attracting electrons in the same energy levels.

1) which of the following is the best example of a physical change? a) sugar dissolving in tea b) firefly glowing 2) in the combustion of ethane, what is/are the reactants? c2h6 + o2 ==> co2 + h2o a) c2h6 and o2 b) co2 and c2h6

Areaction is first order with respect to reactant x and second order with respect to reactant y. which statement describes the rate law for this reaction?