Let's say you hold some ice in your hand. the ice melts and your hand feels cold. is the reaction h2o(s ? h2o(l endothermic or exothermic? is the change in enthalpy of the reaction positive or negative.

Air is to be preheated by hot exhaust gases in a cross-flow heat exchanger before it enters the furnace. air enters the heat exchanger at 95 kpa and 20°c at a rate of 0.6 m^3/s. the combustion gases (cp = 1.10 kj/kg°c) enter at 160°c at a rate of 0.95 kg/s and leave at 95°c. determine the rate of heat transfer to the air and its outlet temperature.