5.1 - Thermochemistry

Energy

The capacity to work or transfer heat.

Work

The energy used to cause an object with mass to move against a force.

Heat

The energy used to cause the temperature of an object to increase.

Joules (J)

The SI base unit of energy.

Kinetic Energy (EK)

The energy of motion.

Thermal Energy

The internal energy of an object based on its temperature, associated with the kinetic energy of the object.

Potential Energy

Energy that is stored; includes forms like electrostatic and chemical energy.

First Law of Thermodynamics

States that energy is conserved in any process; it cannot be created or destroyed.

System

The substances or objects being studied.

Surroundings

Everything outside the system.

Internal Energy (E)

The sum of the kinetic and all potential energies of a substance or object.

Exothermic Reaction

A reaction where the system loses energy, producing heat and transferring it to the surroundings.

Endothermic Reaction

A reaction where the system gains energy, absorbing heat from the surroundings.

Enthalpy Diagrams

Visual representations showing the change in enthalpy during a reaction or process.

Kinetic Energy Formula

The kinetic energy of an object can be calculated using the formula EK = ½ mv².

Thermochemistry

A field of thermodynamics that examines the energy changes in chemical reactions.

Potential Energy Diagrams

Diagrams that show the change in energy from reactants to products in a chemical reaction.

State Function

Property of substance determined by its condition and not how it became in that state

Change in Enthalpy

Constant change of pressure in internal energy

Enthalpy

Measure of energy in thermodynamic system

Constant Pressure Calorimeter

Pressure is same as atmospheric pressure and amount of heat transferred is equal to change in enthalpy

Constant Volume Calorimeter

Measures heat released or absorbed during chemical reaction that occurs at constant volume

Electrostatic Potential Energy

Interaction between two charged objects

Chemical Energy

Energy stored in substances due to arrangement of atoms

Temperature

Average Kinetic Energy of particles in a substance.

Open System

Exchange both energy and matter within surroundings

Closed System

Exchanges only energy within surroundings, not matter

Isolated Systems

Does not exchange either energy or matter within system

• Coffee Cup Calorimeter

Activation Energy

Minimum energy needed for successful collision

What affects rate of reaction

• Changing temperature of reactants

• Changing concentration of reactants

• Changing physical state of reactants

• Adding catalyst

Activated Complex

collides with enough energy to form a complex that can form products

Concentration

increases number of reactant particles and collisions in a given volume

Physical State

Increasing surface area will increase number of available molecules to collide with

Catalysts

Increases number of successful collisions by decreasing amount of energy required during each collision

Biological Catalyst

Enzymes that control rate of reactions in all living things

Reaction Mechanism

step-by-step sequence of elementary reactions by which overall chemical process occurs

Elementary Reactions

one--step reactions, occur in a single event or collision

Reaction Intermediate

produced in earlier step but consumed in a later step

Unimolecular reactions

reaction that involves single reactant molecule

Bimolecular reactions

reactions that involves two reactant molecules

Termolecular reactions

involves three reactant molecules but are very rare

Hess’ Law

Independent to number of steps taken

Supports conservation of energy because it covers initial and final