The temperature of cold packs is lowered when crystals of ammoniumnitrate are dissolved in water. Which of the following is true of thisreaction?
A. ΔH = 0, since cold packs are sealed
B. ΔH > 0, process is exothermic
C. ΔH < 0, process is exothermic
D. ΔH > 0, process is endothermic
E. ΔH < 0, process is endothermic
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Given: 2Al + Fe2O3 → 2Fe + Al2O3 ΔrH = -850 kJWhat is the ΔrH for 4Fe + 2Al2O3 → 4 Al + 2Fe2O3?
A. +850 kJ
B. +1700 kJ
C. -1700 kJ
D. +425 kJ
Reaction rates are affected by concentration, collision geometry,temperature and the presence of a catalyst. Which one of the followingstatements is FALSE?
A. Larger concentrations of reacting particles increase the number ofcollisions.
B. Molecules that do not collide in the correct orientation lower thereaction rate.
C. A catalyst increases the speeds of the reacting particles.
D. Raising the temperature increases the effectiveness of collisions
Which statement explains why the rate of some chemical reactions isincreased when the surface area of the reactant is increased?
A. This change alters the electrical conductivity of the reactant particles.
B. This change increases the density of the reactant particles.
C. This change exposes more reactant particles to a possible collision.
D. This change increases the concentration of the reactant.
解释“G1/2”的含义，查表确定其大经和螺距具体数值。
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