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Chemistry 5
rates
| Question | Answer |
|---|---|
| factors that increase the rate of a reaction 1 | reactants - some substances are more reactive than others surfcae area - break into smaller pieces = more surface to collide w/ concentration - more particles in solu. to collides w/ |
| factors that affect how fast a reaction occurs 2 | temperature - INCREASES BY A LOT - particles move faster & collide more catalyst - provide a new path that doesnt take as much energy - less energy needed = faster rxn |
| factors that affect how fast a reaction occurs 3 | Agitation, brings fresh particles of reactants into contact more often. Pressure(gases only) ' Closer particles, more frequent collisions |
| addition of heat does two things to reactants. What are two things and why does addition of heat cause them? | More collisions and collisions have higher energy. Both happen because particles are moving faster. |
| how does a catalyst work? | Catalyst provides an alternate pathway with a lower Activation Energy |
| how to determine the deltaH and ea for the reverse reaction | deltaH rev = the deltaH with the opposite sign the Ea' = the distance between the product and ea line (alawys +) |
| activation diagrams for reactions | y axis = energy (KJ) x-axis = course of reaction reactants are always at zero the products are at the deltaH the activated complex is on the Ea draw arrow from reactants to products (deltaH) draw from reactants to ea line (ea) |
| how to find the Ea from an activation energy diagram (both forward and reverse) | forward = activated complex - Ereactants reverse = activated complex - Eproducts |
| activated complex | the highest-energy point on the reaction pathway. It exists only for an instant (a vibrational moment). It sits at the top of the E barrier on an E diagram. 'structure that forms when reactants have absorbed enough E to potentially become products. |
| what does it mean if an activation energy diagram has two hills | -two hills represent 2 different steps in the rxn -the rate determining (the slowest step) step is the highest hill - A high activation energy means that fewer particles can collide with enough E to react, making the reaction slower |
| what can be said about Ea and Ea' if a reaction is at equalibrium | -about the same & probably both small activation E must be close in size, -if Ea is different, 1 rxn would move faster → no equilibrium. @ equilibrium, products can react back into react. easily, so E barrier in forward direction can't be big |
| transiton states | The high-energy, unstable arrangement of atoms during the reaction The transition state occurs after the reactants have collided, but before the products are formed. |
| most collisions do not result in a transition state. However, does each hump on the reaction E profile reprensent 1 sucessful collision | no no Even if trillions of molecules are colliding, the energy profile only shows us the energy landscape a single set of molecules must cross to react. It shows the path, not the number of travelers on it. |
| what do the humps on reaction energy diagrams represent | The number of elementary steps (or stages) the reaction takes |
| If an order of zero means that the concentration of a chemical is independent of the rate, then why include it in the equation at all? Why does the chemical still have to be present for the reaction to occur? | it acts at a surface or is always available in excess. -the chemical is not the limiting factor a rxn can happen only on surface of a solid. Once all spots are used up, adding more react. in solution dont increase rate—the max # of rxns is happening |
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Blessed Rectangle 10