1.5 - Kinetics, Equilibria And Redox Reactions Flashcards
How do you calculate rate of reaction?
Amount of reactant used or product formed
/ time
How do reactions occur?
Particles in liquids and gases are always moving and colliding with each other. A reaction will only occur if they collide in the right direction, and with a minimum amount of kinetic energy, which is the activation energy. The particles must have at least this much energy to break their bonds and begin the reaction.
How do you plot a maxwell-Boltzmann distribution curve?
The area under the curve is equal to the total number of molecules. The curve starts at (0,0) because no molecules have zero energy. Most molecules are moving at a moderate speed. The peak of the curve represents the most likely energy of any single molecule. The mean energy is a bit to the right of the peak. Some molecules have more than the activation energy and those are the molecules that will react.
What happens if you increase the temperature on a maxwell boltzmann distribution curve?
Increasing the temp makes the particles have more kinetic energy and move faster. A greater proportion of molecules will have at least the activation energy and be able to react. This moves the shape of the maxwell boltzmann distribution curve to the right and shorter. The total number of molecules will be the same for both reactions so the area will be the same. Frequency of collisions increases and a greater proportion of molecules will have at least the activation energy and be able to react. Thats why small increases in temp lead to large increases in rate.
How does conc and pressure affect rate?
Increasing conc will make the particles closer together and will increase the frequency and likelihood of collisions. Same as pressure.
What is the definition of a catalyst?
Substance that increase the rate of reaction by providing an alternate pathway with a lower activation energy. The catalyst is chemically unchanged at the end of the reaction. In a maxwell boltzmann curve, the Ea will be to the left.
What are the different ways to measure reaction rates?
Timing how long it takes a precipitate to form, but is subjective.
Measuring a decrease in mass. When one of the products is a gas, you can measure the rate of formation using a mass balance. As gas is given off, the mass of the reaction mixture decreases. This method should be done in a fume cupboard. You can measure the volume of gas being produced with a gas syringe.
What happens in the reaction between sodium thiosulfate and HCl.
They are both clear, colourless solutions. They react together to form a yellow precipitate of sulfur. Measure out fixed volumes of sodium thiosulfate and hydrochloric acid using a measuring cylinder. Use a water bath to heat both solutions to the desired temp before u mix them. Mix the solutions in a conical flask, place the flask over a black cross. Time how long it takes for the solution to turn yellow. Repeat at different temperatures. Depth of liquid must be kept the same, same volumes of liquids, same concentrations.
What are the conditions for dynamic equilibrium?
Closed system. Concentrations of reactants and products stay constant. Every species in the same physical state.
How does conc, pressure and temp affect equilibrium?
Increasing the conc of a reactant would shift the equilibrium to the right and make more product. Pressure will only affect equilibria involving gases. Increasing the pressure shifts the equilibrium to the side with fewer moles. Increasing temp will shift equilibrium in the endothermic direction.
How do you find Kc?
If you know the molar concentration of each substance at equilibrium, you can work out Kc. Products divided by reactants. Use ice tables.
What alters Kc?
Temperature. If more product, Kc will rise. Anything else like concentration or catalyst will not affect Kc.
What is oxidation and reduction?
Oxidation is a loss of electrons. Reduction is a gain in electrons.
What oxidation states are oxygen?
Nearly always -2, except in peroxides, where’s its -1. And in the fluorides OF2, where it’s +2, and O2F2 where it’s +1.
What oxidation state is hydrogen?
+1, except in metal hydrides where it’s -1.
Name two differences when magnesium ribbon reacts with hot water compared to when magnesium ribbon reacts with steam.
Faster reaction with steam instead of hot water.
MgO produced with steam but Mg(OH)2 produced with hot water.
Bubbling with hot water but bright white light with steam.
Why would you expect the rate of reaction to double when the concentration of sodium thiosulfate is doubled?
Double the number of particles, double the frequency of successful collisions.
What is rate of reaction?
Change in concentration of a substance in a given time.
Why can 1/t be used as a measure of rate for the thiosulfate reaction?
The amount of precipitate is fixed.
What point do you need to remember when mentioning shifts in equilibrium yield?
Counteracts the change.
State and explain the effect of using catalyst on the yield of methanol in this equilibrium.
No effect on methanol yield as the rate of reaction of both the forward and backwards reactions are increased by the same amount.
What happens if you decrease conc (add water) in an equilibrium mixture?
Favours side with more moles. Acts like pressure.
State, in terms of electrons, the meaning of the term oxidising agent.
Electron acceptor.
Cl2 + H2O <=> HClO + HCl
Give the two half equations
Cl2 + 2H2O -> 2HClO + 2H^+ + 2e-
Cl2 + 2H^+ + 2e- -> 2HCl
