Energy Many forms and sources _________________ is interested in heat exchanges _______ bonds takes energy (___________) _______ bonds produces energy (________) SI Unit is the Joule (J), common unit calorie _____________________ 4.18 kJ = 1 kcal

Temperature and Energy Change Every substance has a unique ability to ______________________________ Called _______________. Water has a very large value. Specific Heat (cp) is the measure of how much ___________ a substance will absorb or release ______________. 4.18J/g°C for water

Q = m cp ΔT Energy = ___________________________ Ex: If 20 g of water changes its temp from 25.0C to 30.0C, what amount of energy is absorbed? Q = (______) x (______) x (_____) Q = 418 J

Heat of Reaction Energy change that occurs during a chemical reaction Called __________ Symbol (____) = change in enthalpy __________ ΔH value = exothermic reaction _________ ΔH value = endothermic reaction

Energy Reactants Products Reaction coordinate ___________ reaction Overall energy change is negative. Products Reaction coordinate

Energy Reaction coordinate Endothermic reaction Overall energy change ____________. Reaction coordinate

Heat of Formation ∆Hf° The energy change associated with the formation of one mole of a _____________________. Sometimes uses fractional coefficients Ex. H2(g) + ½ O2(g) → H2O (l) ∆Hf° = -286 kJ/mol exothermic (comp. is stable) ___________________________ Practice this skill. Important.

Calculation of ΔH reaction Two methods – both work Hess’ Law and a shortcut Learn both (use the shortcut more often)

Hess’ Law - finding ΔH Says that if you can write a reaction in steps that add up to the original reaction, ____ ______________ is the sum of the ΔH of the steps. (route independent) Guidelines 1. If the reaction is reversed, so is the sign of ΔH. 2. If coefficients are multiplied, so is ΔH.

Example: find ΔH CH4(g) + 2O2(g) → CO2(g) + 2H2O(l) Solution 1. Write ΔHf eq. for each compound C(s) + 2H2(g) → CH4(g) ΔH = -74.8 kJ C(s) + O2(g) → CO2(g) ΔH = -393.5 kJ H2(g) + ½ O2(g) → H2O(l) ΔH = -285.8 kJ

ALTERNATIVE TO HESS’ LAW Handy shortcut to use for calculations. ΔH = Σ ΔHf (products) - Σ ΔHf (reactants) Remember to ________________________ in the balanced equation. ΔH = (-393.5 kJ + _________) – (-74.8 kJ) ΔH = ________

________________ REACTIONS Proceed without outside assistance (beyond the initial Ea) -- they just happen. Spontaneous chemical reactions generally occur if the ____________________________________. -sometimes this is not the case ( ex---H2O(s) only forms if the temp is less than 0C) -reason for this is the other driving force in nature...........

Entropy A ___________________ or randomness of a system. -represented by S (_______________) ΔS = __________________________

All entropies (Sf and Si) are positive, but …ΔS can be negative or positive. if ΔS is negative ===> _______________ (lower entropy) Example: ______________ of a liquid if ΔS is positive ===> _____________ (more entropy) Example: ___________ of a liquid….. favored in nature!

Prediction of entropy change _______________ of compounds decreases entropy (due to bonding) decomposition of compounds ________ entropy mixing a solute and solvent __________ entropy Solid→ Liquid → Gas ___________ entropy Ie. __________ of a liquid increases entropy

So>>>>>> Two forces influence the direction of a spontaneous reaction: ΔH and ΔS when ΔH decreases; _________________. when ΔS increases; __________________

Gibbs Free Energy ΔG An equation called the “Gibbs equation” compares the values of ΔH and Δ S. __________________ if _____________; the reaction is spontaneous if _____________: the reaction is not spontaneous, and will not occur.

4 Possible Cases ΔH ΔS Result: + reaction favored - ____________ - ____________ - rx if ΔH is large + rx if ΔS is large *****Alternative to the Gibbs equation: ΔG = ΣΔGf (products) - ΣΔGf (reactants)

Collision Theory In order to react molecules and atoms must touch each other. They must hit each other hard enough to react. Anything that increase these things will make the reaction faster.

Things that Effect Rate ____________________ Higher temperature = faster particles. More and harder collisions. Faster Reactions. More concentrated = molecules closer together. Collide more often. Faster reaction.

Things that Effect Rate ___________________ Molecules can only collide at the surface. Smaller particles = bigger surface area. Smaller particles = faster reaction. Smallest possible is atoms or ions. Dissolving speeds up reactions. Getting two solids to react with each other is slow.

Things that Effect Rate _____________- substances that speed up a reaction without being used up.(enzyme). Speeds up reaction by giving the reaction a new path. The new path has a__________________. More molecules have this energy. The reaction goes faster. ____________- a substance that blocks a catalyst.