Instant Hot and Cold Packs Commercial instant cold packs typically use either ammonium nitrate or urea as their salt component; hot packs often use magnesium sulfate or calcium chloride. These reactions happen in a similar manner. When the salt is dissolved in water, the ionic bonds of the salt separate.

A hot pack is produced if an exothermic reaction occurs as the salt and water mix and heat energy is released because this process will raise the temperature of the contents in the pack.

Heat packs that contain iron and water packets: Exposing the solution to air results in the oxidation of the iron (creates rust). The oxidation of the iron is an exothermic process. Heat packs that contain supersaturated sodium acetate: These are reusable, the packs are boiled to dissolve sodium acetate.

An exothermic process releases heat, causing the temperature of the immediate surroundings to rise. An endothermic process absorbs heat and cools the surroundings.”

BREAKING AND FORMING BONDS Bond breaking is an endothermic process, because it requires energy. Bond forming is an exothermic process, because it releases energy.

Chemical reactions that release energy are called exothermic. In exothermic reactions, more energy is released when the bonds are formed in the products than is used to break the bonds in the reactants. Exothermic reactions are accompanied by an increase in temperature of the reaction mixture.

If the temperature is increasing, a product is being added to the equilibrium, so the equilibrium shifts to minimize the addition of extra product: it shifts back toward reactants. However, a catalyst does not affect the extent or position of a reaction at equilibrium. It helps a reaction achieve equilibrium faster.

Therefore if the reaction is exothermic as written, an increase in temperature will cause the reverse reaction to occur, decreasing the amounts of the products and increasing the amounts of reactants. Lowering the temperature will produce the opposite response.

RAISING THE TEMPERATURE INCREASES Keq FOR AN ENDOTHERMIC REACTION AND LOWERS Keq FOR AN EXOTHERMIC REACTION (LOWERING THE TEMPERATURE HAS THE OPPOSITE EFFECT.) Ea2 < Ea1 so the right side of the equation is positive.

Phases and Phase Transitions

The effect of increasing temperature When the temperature is increased, the position of equilibrium moves in the endothermic direction to reduce the temperature. This means that as the temperature is increased, the position of equilibrium moves to the left, and the yield of ammonia decreases.

Endothermic reactions are the opposite of exothermic reactions. They absorb heat energy from their surroundings. This means that the surroundings of endothermic reactions are colder as a result of the reaction. Melting ice is an example of this type of reaction.

It took energy to break the baking soda and vinegar apart and energy was released when the carbon dioxide, sodium acetate, and water were formed. Since more energy was needed to break the baking soda and vinegar apart, the temperature went down. This reaction is called an endothermic reaction.