chemical energetics Flashcards
Thermodynamics
the science of the relationship between heat, work, temperature, and energy. thermodynamics transfers energy from one place to another and from one form to another. The key concept is that heat is a form of energy corresponding to a definite amount of mechanical work.
The First Law of Thermodynamics
The Law of Conservation is the energy which can neither be created nor destroyed. Instead, energy can only be transferred or changed from one form to another. If a chemical reaction occurs, total energy of the reactants must equal the total energy of the products and any energy lost to (or gained from) the surroundings
Enthalpy
the energy of a substance under constant atmospheric pressure
The enthalpy of elements and compounds cannot be calculated, but enthalpy changes (∆H), are easily measured.
If a chemical or physical change occurs at constant pressure, the amount of heat energy
absorbed or produced in the change equals the change in enthalpy that has taken place.
Exothermic Reaction
enthalpy changes, ∆H is negative because exothermic reaction energy moves from heat to the surroundings. This loss of energy shows that the reactant molecules were at a higher level of enthalpy than the product molecules. If an exothermic reaction occurs in a container and you are holding it, the reaction mixture will be hot to touch.
Endothermic Reaction
Enthalpy changes, ∆H is positive because endothermic reaction energy is taken in from the surroundings to heat. This gain of energy shows that the reactant molecules were at a lower level of enthalpy than the product molecules. If an endothermic reaction occurs in a container and you are holding it, the reaction mixture will be cool or cold to the touch.
the standard enthalpy change of reaction 정의
The enthalpy change of a reaction when the reactants and products are in their standard states. A substance is said to be in its standard state when it is in pure form at an atmospheric pressure of 1 atm (101 kPa). Temperature is not part of the definition here.
If the sum of the bond enthalpies of the product molecules is greater than the sum of the bond enthalpies for the reactants, the reaction will be exothermic.
If the sum of the bond enthalpies of the product molecules is less than the sum of the bond enthalpies for the reactants, the reaction will be endothermic.
Hess’s Law
Hess’s Law states that if a reaction can occur by more than one route, the enthalpy change is the same, whichever route is followed.
catalysis definition + difference between homogenous and heterogenous of catalyst
A catalyst is a substance which increase the rate of a reaction but is chemically unchanged at the end of the reaction.
Catalysts work by providing an alternative reaction pathway with a lower activation energy than that of the original reaction, which requires more molecules to collide with success
Homogenous catalysts are in the same phase /state as the reactants.
Heterogenous catalysts are in a different phase to the reactants
enzyme carbonic anhydrase
The enzyme carbonic anhydrase catalyses the reversible reaction of carbon dioxide and water to form carbonic acid.
When the concentration of carbon dioxide in the body is too high, carbonic anhydrase catalyses the following reaction:
CO2 + H2O → H2CO3
By regulating the concentration of carbonic acid in the blood and tissues, the enzyme is able to keep the pH balanced in the body.
standard enthalpy of combustion
The energy/enthalpy change when 1 mole of a substance is completely combusted in oxygen. All substances in their standard stated at 298K 1 atm pressure
