Identify each energy exchange as primarily heat or work and determine whether the sign of δe is positive or negative for the sys
tem. a. sweat evaporates from skin, cooling the skin. (the evaporating sweat is the system.)
b. a balloon expands against an external pressure. (the contents of the balloon is the system.)
c. an aqueous chemical reaction mixture is warmed with an external flame. (the reaction mixture is the system.)
Heat is released in an exothermic reaction and heat is absorbed in an endothermic reaction.
Heat is negative for an exothermic reaction and it is positive for an exothermic reaction.
Work done by a system is positive and work done on the system is negative.
a. The evaporating sweat is the system. Here the sweat absorbs heat to make the phase transition from liquid water to vapor. The reaction is endothermic and the heat is positive.
b. The balloon (system) does work to expand against an external pressure. As the work is done by the system it is positive.
c. As the chemical reaction is warmed it has absorbed heat. The reaction is endothermic and the heat is positive.
At the eutectic composition, an alloy can solidify at a constant temperature : TRUE . this is because at eutectic composition the type of reaction that takes place there is invariant reaction in its thermal equilibrium
For effective dispersion strengthening, the dispersed phase should be needle-like, as opposed to round : FALSE. because the rounded shape will not cause a crack.
Intermetallic compounds are usually hard and brittle : TRUE. because Intermetallic compounds prevents dislocation movements and this makes them brittle and hard
For the effective dispersion and strengthening, the dispersed phase should be continuous : FALSE. this is because the dispersed precipitate must be small and not continuous
Stoichiometric intermetallic compounds exist over a range of compositions : FALSE
Faster solidification results in smaller interlamellar spacing : TRUE
