Question

identify the endothermic processes. check all that apply.
mg(s) + 2 h₂o(l) → mg(oh)₂(s) + h₂(g) + 84.3 kcal
2 hbr(g) + 72.4 kj → h₂(g) + br₂(l)
h₂(g) + i₂(s) + 53. kj → 2 hi(g)
2 so₂(g) + o₂(g) → 2 so₃(g) + 198. kj
h₂so₄(l) + 132.5 kj → so₃(g) + h₂o(l)
none of the above

Explanation:

Step1: Recall endothermic definition

Endothermic processes absorb energy (energy on reactant side, +energy in reactants or -energy in products).

Step2: Analyze each reaction

• Reaction 1: $\ce{Mg}(s) + 2\ce{H2O}(l)

ightarrow \ce{Mg(OH)2}(s) + \ce{H2}(g) + 84.3$ kcal. Energy is a product (released), exothermic.

• Reaction 2: $2\ce{HBr}(g) + 72.4$ kJ $

ightarrow \ce{H2}(g) + \ce{Br2}(l)$. Energy is a reactant (absorbed), endothermic.

• Reaction 3: $\ce{H2}(g) + \ce{I2}(s) + 53.$ kJ $

ightarrow 2\ce{HI}(g)$. Energy is a reactant (absorbed), endothermic.

• Reaction 4: $2\ce{SO2}(g) + \ce{O2}(g)

ightarrow 2\ce{SO3}(g) + 198.$ kJ. Energy is a product (released), exothermic.

• Reaction 5: $\ce{H2SO4}(l) + 132.5$ kJ $

ightarrow \ce{SO3}(g) + \ce{H2O}(l)$. Energy is a reactant (absorbed), endothermic.

Answer:

The endothermic processes are:

• $2\ce{HBr}(g) + 72.4$ kJ $

ightarrow \ce{H2}(g) + \ce{Br2}(l)$

• $\ce{H2}(g) + \ce{I2}(s) + 53.$ kJ $

ightarrow 2\ce{HI}(g)$

• $\ce{H2SO4}(l) + 132.5$ kJ $

ightarrow \ce{SO3}(g) + \ce{H2O}(l)$

(Check the boxes for these three reactions.)