Thermochemistry – Endothermic and Exothermic Reactions

Flashcards covering key definitions, concepts, examples, and applications of endothermic and exothermic reactions in thermochemistry.

What does thermochemistry study?

The heat changes that occur during chemical reactions.

What is an exothermic reaction?

A reaction that releases heat to the surroundings, causing the temperature to rise.

What is an endothermic reaction?

A reaction that absorbs heat from the surroundings, causing the temperature to drop.

What does the Greek prefix “exo-” mean?

“Outside.”

What does the Greek prefix “endo-” mean?

“Inside.”

How can you quickly identify whether a reaction is exothermic or endothermic?

Detect the temperature change: if it becomes hot it’s exothermic; if it becomes cold it’s endothermic.

Which device is commonly used to measure temperature changes in chemical reactions?

A thermometer.

During an exothermic reaction, what happens to the temperature of the reaction container?

It increases and feels hot.

During an endothermic reaction, what happens to the temperature of the reaction container?

It decreases and feels cold.

In energy terms, what occurs in an exothermic reaction?

Chemical energy in the reactants is converted to heat energy and released to the surroundings.

In energy terms, what occurs in an endothermic reaction?

Heat energy is absorbed from the surroundings and stored in the products.

What are reactants?

Substances that start a chemical reaction.

What are products in a chemical reaction?

Substances that are formed as a result of the reaction.

Which type of reaction occurs when sodium metal reacts with water?

An exothermic reaction that produces sodium hydroxide and hydrogen gas.

Why do instant hot packs relieve muscle cramps?

They undergo an exothermic reaction that releases heat, warming muscles and dilating blood capillaries to improve circulation.

Why are instant cold packs used for swelling?

They undergo an endothermic reaction that absorbs heat, lowering tissue temperature, reducing blood flow, swelling, and pain.

Give three everyday examples of exothermic processes.

Burning paper, bomb explosions, respiration (cellular).

Give three everyday examples of endothermic processes.

Photosynthesis, melting ice, evaporation of water.

Is condensation an exothermic or endothermic process?

Exothermic; it releases heat as gas turns to liquid.

Is photosynthesis exothermic or endothermic, and why?

Endothermic; it absorbs light energy to convert CO₂ and water into sugar.

When sodium hydroxide pellets dissolve in water, is the process exothermic or endothermic?

Exothermic; it releases heat and raises the solution’s temperature.

Is heating calcium carbonate (thermal decomposition) exothermic or endothermic?

Endothermic; heat is absorbed to decompose calcium carbonate.

Classify the reactions: (a) HCl + Na₂CO₃, (b) HCl + NaHCO₃.

(a) Exothermic, (b) Endothermic.

How does heat from an exothermic hot pack affect blood capillaries?

It dilates (widens) the capillaries, increasing blood flow.

What is thermal equilibrium?

A state in which two objects in contact no longer exchange heat because they are at the same temperature.