Thermochemistry: The heat energy of chemical reactions • Enthalpy is the amount of ________ transferred during a reaction. The symbol for the change in enthalpy is ∆H. An endothermic reaction is one that ___________ heat from the surroundings. (___ ∆ H) An endothermic reaction feels ______. Example--an “instant” ice pack • An exothermic process is one that _____________ heat to the surroundings. (___ ∆ H) An exothermic reaction feels _____. Example--burning paper gains + cold loses – hot

Phase Changes & Energy Endothermic: melting, evaporating/boiling & sublimation Exothermic: freezing, condensation, & deposition

Endothermic Exothermic

Chemical Kinetics fast concentration Temperature Enzymes Surface Kinetics is the study of how _____ chemical reactions occur. There are 4 important factors which affect rates of reactions: reactant ______________ ________________ action of catalysts (________________are biological catalysts.) ___________ area For the reaction “A  B” there are two ways of measuring rate: (1) the speed at which the reactants ____________ (2) the speed at which the products __________ In general, rates of reactions _________ as concentrations increase since there are more _____________ occurring between reactants. concentration Temperature Enzymes Surface disappear appear increase collisions

Catalysts and Reaction Rates

Chemical Equilibrium equals dynamic constant Some reactions are reversible, so as products accumulate they can begin to turn back into reactants. When the rate of the forward reaction ____________ the rate of the reverse reaction, it is at equilibrium. Here’s an example: Each is constantly being formed at the same rate that it is being consumed. It is therefore called a “_____________ equilibrium”. Chemical equilibrium is the point at which the concentrations of all species are ________________. equals dynamic constant

Dynamic Equilibrium

Changes in Equilibrium Le Chatelier’s Principle: If a stress is applied to a system that is already at equilibrium, the equilibrium will shift to reduce the effect of the stress. We will now look at changing various things on a system at equilibrium. Consider this reaction: A + B C + D Here are some things that one can change in order to shift the equilibrium: (1) Changing _______________________ of the Solutions (2) Changing the _____________________ of the Gases (3) Changing the _____________________ Adding a catalyst ________ _______shift the equilibrium. It just makes the reaction achieve equilibrium ______________. Concentration Pressure Temperature does not faster

Changes in Equilibrium For the reaction below, predict the direction the equilibrium will shift given the following changes. Temperature and volume are held constant. Fe3+(aq) + SCN–1(aq) FeSCN2+(aq) (colorless) (red) More Fe3+ is added to the reaction. ____________________ - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - NO2 (g) + 7 H2 (g) ↔ 2 NH3 (g) + 4 H2O(g) Predict the shift in equilibrium given the following changes: a. addition of ammonia ____________________ b. removal of nitrogen dioxide ____________________ c. removal of water vapor ____________________ d. addition of a catalyst ____________________ Shifts to the right (…more red) Shifts to the left Shifts to the left Shifts to the right No change

Catalysts & Changes in Equilibrium