Chem Unit One Enthalpy Change

Study of energy changes by a chemical system during a reaction.

Process used to measure the energy changes inside an isolated system called a calorimeter.

• -Thermal energy is the total kinetic energy of its entities.
• - heat is the transfer of thermal energy
• -Temperature is the measurement of average kinetic energy of entities.

The chemical system inside the calorimeter releases energy as heat which is absorbed by the surroundings (water) this results in the temperature of the calorimeter rising. Here the system loses potential energy, and the calorimeter gains kinetic energy.

The chemical system absorbs energy in the form of heat from the surroundings/calorimeter resulting in the temperature of the calorimeter to drop. The system gains potential energy and the calorimeter loses thermal energy. Ek=-Ep

It is the total kinetic and potential energy within a chemical system.

it is the difference between the enthalpy of the products and the enthalpy of the reactants.

Due to the conservation of energy in an isolated system. The calorimeter cannot gain kinetic energy with ought the chemical system losing potential energy and vice versa.

It states that you can calculate the enthalpy change of a reaction by breaking it down into smaller steps, each with its own molar enthalpy change, each with its own enthalpy change, and then add them all up to find the overall centhalpy change.

tendency of compounds to resist decomposition when heated. the greater the standard molar enthalpy, the greater the thermal stability.

• used to explain and predict characteristics of chemical reactions. Main ideas:
• -chemical samples have entities in them that are always moving
• -a chemical reaction must have collisions of reactant entities.
• -to have an effective collision, there must be sufficient energy and the correct orientation of colliding entities to react and form new bonds.

An energy barrier that must be overcome for a chemical reaction to take place. it is also the difference between the reactants and the activated complex.

when the reaction happens rapidly and at room temperature because the reactants can easily turn into the products withought much energy needed.

the chemical entity where the reactants collide.

Two reactant molecules collide with sufficient energy and the correct orientation to achieve the activated complex and the reaction starts. From there, potential energy of the product molecules decrease until (if endothermic) the final potential energy is greater than the initial or (if exothermic) the initial potential energy is greater than the final.

To form the activated complex, the kinetic energy of the reactant molecules must be converted to potential energy within the activated complex. the activated complex then breaks into the product entities, converting the potential energy back into kinetic energy. Now since this reaction is endo thermic, there will be less kinetic energy and more potential energy in the products than in the reactants.

the energy required to break a chemical bond and it is also the energy released when a bond is formed.

the activation energy is the amount of energy required to break the initial bonds in the reactant entities.

quantitty of energy required to break the H-O bonds is greater than the quantity of energy required to form the H-H bonds and the O-0 bonds in the products.

substance that increases the rate of chemical reaction.

• -They are not consumed or changed in any way in the overall process.
• -The reduce activation energy but don't affect the enthalpy change.
• -They allow reactions to produce the same products as an uncatalyzed reaction in shorter periods of time and at lowere temperatures.

provides an alternative lower energy pathway from reactants to products. The catalyst allows the reaction to occur through a different activated complex. if the new pathway has a lower activation energy, more molecules possess the minimum required energy so the reaction rate increases.