HChemistry - Endothermic & Exothermic - Reactions

What is chemical energy (Ech)?

Chemical energy (Ech) is potential energy stored in chemical bonds.It comes from energy transferred from the surroundings into bonds or released when bonds form.

What is thermal energy (Eth)?

Thermal energy (Eth) is the energy of particle motion. Faster-moving particles = higher Eth.

What does temperature measure?

Temperature measures the average kinetic energy (motion) of particles.

Higher temperature = particles moving faster.

How does energy move to reach thermal equilibrium?

Energy transfers from warmer → cooler areas until thermal equilibrium is reached.

This transfer often goes into chemical bonds (Ech) or particle motion (Eth).

How do particle collisions help reactions occur?

More kinetic energy → more collisions → atoms rearrange → old bonds break → new bonds form.

As energy is used, particle motion slows and the system reaches thermal equilibrium.

What does exothermic mean?

Exothermic means energy is released.

Think exo = exit → energy exits the system to the surroundings.

What does endothermic mean?

Endothermic means energy is absorbed.

Energy enters the system from the surroundings.

What is the energy flow in an exothermic reaction?

System → Surroundings

Energy leaves the system as thermal energy (Eth).

What is the energy flow in an endothermic reaction?

Surroundings → System

Energy is absorbed and stored in chemical bonds (Ech).

What is the definition of an exothermic reaction?

A reaction is exothermic if the solution becomes warmer, meaning energy flows from the reaction system to the cooler surroundings.

What are the energy changes in an exothermic reaction?

Energy is released and considered part of the products.

The Ech of the reactants is higher than the Ech of the products.

What is the exothermic energy bar diagram (Ech)?

Reactants: 4 bars

Products: 2 bars

The difference is energy released as Eth to the surroundings.

Why does temperature increase in an exothermic reaction?

As new bonds form, excess energy is released as thermal energy (Eth), raising the temperature of the system and/or surroundings.

What is the exothermic Ech explanation?

The Ech of the reactants drops to the lower Ech of the products, showing the energy released to the surroundings.

What is the definition of an endothermic reaction?

A reaction is endothermic if heating the reactants causes the reaction, meaning energy flows from warmer surroundings into the cooler system.

What are the energy changes in an endothermic reaction?

Energy is absorbed from the surroundings and stored in chemical bonds.

The Ech of the reactants is lower than the Ech of the products.

Energy is conserved.

Why is heating needed for endothermic reactions?

Heating increases particle motion, allowing collisions that rearrange atoms and break bonds so new bonds can form.

What is the endothermic Eth explanation?

Energy transferred through collisions increases the system's Eth, which is then stored as Ech in the products' bonds.

How is Eth stored?

Eth is stored as kinetic energy of particles: vibrations, rotations, and translations.

How is Ech stored?

Ech is stored as potential energy in chemical bonds, related to electron positions.

What is the role of Eth in endothermic reactions?

Energy from the surroundings increases Eth, helping bonds break and atoms rearrange.

What is the role of Eth in exothermic reactions?

Eth increases the temperature of the surroundings

Energy released by the system increases the Eth of the surroundings, raising temperature.

What is the comparison of Ech in exothermic vs endothermic?

Exothermic: Ech decreases → Eth released Endothermic: Ech increases → energy absorbed

What is the temperature change in exothermic reactions?

Temperature increases.

The system feels warm or hot.

Why does temperature rise in exothermic reactions?

Energy released from bond formation becomes Eth, increasing particle motion.

What is the temperature change in endothermic reactions?

Temperature decreases unless heat is added. The system may feel cold.

Why does temperature drop in endothermic reactions?

Energy is absorbed and stored as Ech, leaving less Eth in the system.

What is a one-line comparison of exothermic vs endothermic?

Exothermic: temperature ↑, energy out; Endothermic: temperature ↓, energy in.

What is a quick memory tip for Eth vs Ech?

Eth = motion of particles (hot/cold)

Ech = energy in bonds (stored/released)