超星 - Module 4 quiz and assignment

单选题

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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单选题

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

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单选题

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

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单选题

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.

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单选题

When ΔH is negative, which of the following is correct in terms of the heatexchanged?

A. The heat is a reactant.
B. The heat is a product.
C. The heat is neither a reactant nor product
D. The heat is both a reactant and a product

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