Moth balls gradually vaporize, is this a physical change?

Which type of reaction always has an element and a compound as reactants

Which compound contains both ionic and covalent bonds? a) hbr b)cbr4 c)nabr d) naoh

Voltaic cells produce a positive overall charge. what does this indicate? a. the reaction is likely to be endothermic. b. the reaction is spontaneous. c. the reaction is not likely to occur. d. the reaction is not spontaneous.