Reactivity 1.1: Types of energy change

Define exothermic reaction

heat is released by/ transfer of thermal energy from the system to the surroundings
(exo cause exo 멤버들 계속 탈퇴)

Examples of exothermic reactions

• combustion

• condensation

• deposition

State the characteristic of exothermic reactions’ enthalpy change

negative

Define enthalpy

measurement of energy in a thermodynamic system
(energy content of a system)

Define system

• all components that participate in a chemical reaction (ex. reactants, products, catalysts, etc.)

• Contents of a flask

Explain the change in enthalpy ΔH

• negative → heat removed from the system

• positive → heat added to the system

• look at this from the point of view of a system

(If you have a negative of something, you don’t have it or you lose it. If you have a positive of something, you have it or you gain it.)

State the characteristic of a positive ΔH in terms of stability

products’ bonds are relatively more unstable

State the characteristic of a negative ΔH in terms of stability.

products’ bonds are relatively more stable

Exothermic reaction enthalpy change diagram

energy graph (y axis: enthalpy, x axis: reaction)

Define endothermic reactions

heat is absorbed by the system from the surroundings

State examples of endothermic reactions

• photosynthesis

• dehydration of hydrates

• melting

• vaporization

• sublimation

State the enthalpy change ΔH for endothermic reactions

positive

Describe open system

Transfer of energy and matter is possible across its boundary

• matter can be added or removed

• energy can be transferred outside of its container

Describe closed system

No matter is transferred; energy is transferred across its boundary

• matter cannot be removed or added

• energy can be transferred in our out the container

Describe isolated system

No matter or energy can enter nor exit the system

State the equation for ΔT

T_final - T_initial

Define heat (q)

energy that is transferred from a warmer body to a cooler body, as a result of the temperature gradient

Define temperature gradient

Explain the difference between temperature and heat