Which statement best rationalizes /\ssys for combustion of methane ch4(g)+2o2(g)→co2(g)+2h2o(g) a. there is a combustion reaction, so /\ssys will be a large negative number.
b. there are no changes os state and no change in nrxn so /\ssys will be small
c. combustion reactions are exothermic, so /\ssys also will be a large negative number
d. this is a combustion reaction so /\ssys will be a large positive number

An unknown substance is a white solid at room temperature and has a melting point of 78 °c. which of the following substances is most likely to be the identity of the unknown sample? a. naphthalene, a molecular solid with the formula c10h8 b. silica, a network solid held together by covalent bonds with the formula sio2 c. calcium chloride, an ionic compound with the formula cacl2 d. water, an molecular compound with the formula h2o