How to solve

General Chemistry

Chapter $7$ Worksheet Part $1$

Energy

Describe potential energy and kinetic energy and give examples of each.

Define spontaneous. List two common reactions or processes that are spontaneous.

Define nonspontaneous. List two reactions or processes that are nonspontaneous.

Define bond dissociation energy.

Question $5-9$ refer to the following reaction.

Some types of hand warmers and warming pads use a slow combustion $($oxidation$)$ reaction. The same reaction occurs when rust forms in a drainpipe or on your bicycle.

$4Fe(s)+3O_2(g)2F{e}_2{O}_3(s)+$ heat $H=-1650kJ$

If you open a packet of hand warmers and expose them to oxygen in the air, you will feel the hand warmers becoming warm. Define spontaneous. Is the hand warmer a spontaneous reaction?

Given the value for $H$ for the reaction, is this an example of an exothermic or an endothermic reaction?

$1$

Describe the heat flow between the system $($heat pack$)$ and the surroundings $($your hand$).$ Is the pack taking your heat, or is it making your hand warmer?

Examine the moles of reactants and products and the state of matter for each. Is entropy increasing or decreasing in this reaction? What is the sign of $S?(+$or$-)$

Find $G$ for the above reaction at $298K$ using the Gibbs Free energy equation.

$G=H-(T*S)$

$S=-0\mathrm{.}550k\frac{J}{K}$

$H=-1650kJ$

Question $10-14$ refer to the following reaction:

Ammonium nitrate $(N{H}_{4}N{O}_3),$ which is found in cold packs, is often used in fertilizers. In cold packs, it reacts with heat from the surroundings in the presence of water to dissociate into ammonium and nitrate ions.

$H_{2}O$

$N{H}_{4}N{O}_3(s)+$ heat $N{H}_4^{+}(aq)+N{O}_3^{-}(aq),H=+28kJ$

If you break open the water packet inside the cold pack and allow the ammonium nitrate and water to mix, you will feel the cold pack becoming cold. Is this reaction spontaneous? Explain, using the definition of spontaneous.

Given that the $H=+28\mathrm{.}0kJ$ for the reaction, is this an example of an exothermic or endothermic reaction? How do you know?

Why does the cold pack get cold? Explain your answer in terms of heat flow between the system and the surroundings.

Examine the moles of reactants and products and the states of matter for each. Is entropy increasing or decreasing for this reaction? What is the sign of $\frac{?}{{?}_{\frac{?}{?}}S}?$

Find $G$ for the above reaction at $298K$ using the Gibbs Free energy equation.

$G=H-(T*S)$

$S=+0\mathrm{.}107k\frac{J}{K}$

$H=+28\mathrm{.}0kJ$