A student is analyzing an unknown substance. The substance is solid at room temperature, but when heated only slightly, it melts. It boils when placed over a flame for more than a few seconds. The student dissolves the substance in water and finds the solution does not conduct electricity. Based on the experimental evidence, how should the student categorize the molecules that make up this substance? A:ionic compounds

B:transition metals

C:radioactive

D:covalent compounds

Using this reversible reaction, answer the questions below: n2o4 2no2 (colorless) (reddish-brown) -as the temperature increased, what happened to the n2o4 concentration? -was the formation of reactants or products favored by the addition of heat? -which reaction is exothermic? right to left or left to right? -if the change of enthalpy of this reaction when proceeding left to right is 14 kcal, which chemical equation is correct? n2o4 2no2 + 14 kcal n2o4 2no2, hr = +14 kcal n2o4 + 14 kcal 2no2 n2o4 2no2, hr = -14 kcal