Unit 9 - Thermochemistry Flashcards
Thermochemistry
The study of energy changes during a chemical reaction or change of state (solid, liquid, gas).
Chemical Potential Energy
The energy stored in chemical bonds. (Lines with no Slope on the Heating Curve)
Heat
Energy that transfers from one object to another due to a difference in temperature between them. Heat always flows from the warmer to the cooler object.
Melting
Make or become liquefied by heat. (Solid to Liquid)
Freezing
Freezing or solidification is a phase transition in which a liquid turns into a solid when its temperature is lowered below its freezing point. (Liquid to Solid)
Condensation (Precipitation)
The conversion of a vapor or gas to a liquid.
Vaporization (Evaporation)
The conversion of a liquid into a gas.
Heat of Fusion
The energy required to change a gram of a substance from the solid to the liquid state without changing its temperature.
Solidification
Freezing or solidification is a phase transition in which a liquid turns into a solid when its temperature is lowered below its freezing point. (Liquid to Solid)
Heat
A form of energy that flows between two samples of matter because of their differences in temperature.
Temperature
A measure of the intensity of heat, i.e. the hotness or coldness of a sample. or object.
Kinetic Energy
In Thermochemistry, the energy an object possesses due to its change in temperature is called kinetic energy. (Sloped lines on the Heating Curve)
Potential Energy
Potential energy is that energy which an object has because of its position. It is called potential energy because it has the potential to be converted into other forms of energy, such as kinetic energy. (Lines with no Slope on the Heating Curve
Endothermic
Reaction in which the system absorbs energy from its surroundings in the form of heat.
Exothermic
An exothermic reaction is a chemical reaction that releases energy in the form of light or heat.
Activation Energy
The minimum energy required to start a chemical reaction
Collision Theory
Molecules have to collide in a certain way with a certain amount of activation energy in order to form a new product.
Heating Curve
A plot of the temperature versus time.
How to speed up the Rate of a Reaction
- Shrink the container or increase concentration. 2. Increase the number of particles. 3. Speed up the particles by adding heat. 4. Break up clumps into individual particles. 5. Use a catalyst.
Catalyst
A substance that causes a chemical reaction to happen more quickly.
Solid
Solid is one of the four fundamental states of matter. It is characterized by structural rigidity and resistance to changes of shape or volume.
Liquid
Liquid is one of the four fundamental states of matter, and is the only state with a definite volume but no fixed shape. A liquid is made up of tiny vibrating particles of matter, such as atoms, held together by intermolecular bonds.
Phase Changes
Gas
One of four main states of matter, composed of molecules in constant random motion. Unlike a solid, a gas has no fixed shape and will take on the shape of the space available. Unlike a liquid, the intermolecular forces are very small; it has no fixed volume and will expand to fill the space available.
Boiling
Boiling is the rapid vaporization of a liquid, which occurs when a liquid is heated to its boiling point.
Boiling Point
The temperature at which the vapor pressure of the liquid is equal to the pressure exerted on the liquid by the surrounding environmental pressure. At the boiling point the gas and liquid phase exist in equilibrium.
Evaporation versus Boiling
Melting Point
The melting point of a solid is the temperature at which it changes state from solid to liquid at atmospheric pressure. At the melting point the solid and liquid phase exist in equilibrium.
Law of Conservation of Energy
Energy can not be created nor destroyed during a chemical reaction
Heat Capacity
Heat capacity is the amount of heat energy required to change the temperature of a substance
Endo or Exothermic?
Exothermic reaction graph
Phase Diagram most substances (e.g. CO2)
slight positive slope; more dens in (l) phase;
triple point: s, l, g in equilib.
critical point: T and P above which there is no distinction between l and g
Phase Diagram H2O
negative slope bc H2O has lower density in (s) than (l); increase in P favors more dense version.
Which phase changes are endothermic? Which are Exothermic? Is bond breaking Endothermic or Exothermic?
Phase Diagram Questions
Heating Curve Questions
thermochemical equation
thermochemical equation
- balanced chemical equations with heat changes taken into account
- think of it as (and treat it as) a reactant or a product
Enthalpy (H)
-the heat content of a system (or chemical reaction)
CaO (s) + H₂O (l) → Ca(OH)₂(s) + 65.2 kJ
Change in H = - 65.2 kJ
Endo or Exo?
Exo
heat is a product and change in H is negative
2 NaHCO₃ (s) + 129 kJ → Na₂O (s) + H₂O (g) + CO₂(g)
Change in H = +129 kJ
Endo or Exo ? How to tell?
Endo
heat is a reactant and change in H is positive
five ways to tell if a reaction is exothermic
graph slopes down
heat is given off (to the surroundings)
change in H is negative
temperature of “surroundings” increases
heat is written as a product
five ways tell if a reaction is endothermic
graph slopes up
heat is absorbed (from the surroundings)
change in H is positive
temperature of “surroundings” decreases
heat is written as a reactant
