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Description
Flashcards by Kayla Price, updated more than 1 year ago
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Created by Kayla Price
over 7 years ago
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| Question | Answer |
| What is dynamic equilibrium? | When the rate of the forward reaction is equal to the rate of the reverse reaction |
| What is a homogeneous system? | A system in which everything is in the same physical state |
| What is a heterogeneous system? | A system in which not everything is in the same physical state |
| What is not included in the Kc expression for a heterogeneous equilibria and why? | Solids and liquids because their concentrations stay constant |
| How would you write a Kc expression? | Conc. products over conc. reactants to the power of the number of moles of each |
| Why are catalysts not included in the Ka expression? | They do not affect the equilibrium concentrations and therefore the position of equilibrium, they just increase the rate at which dynamic equilibrium is met |
| State Le Chatelier's Principle | If there is a change in concentration, pressure or temperature, the position equilibrium will shift to counteract the change |
| What are partial pressures? | Pressures of individual gases - the sum of which is equal to the total pressure |
| How would you find the mole fraction of a gas? | Number of moles / total number of moles |
| How would you find the partial pressure of a gas? | Mole fraction x total pressure |
| How is Kp calculated? | Partial pressure of products over partial pressure of reactants each to the power of number of moles |
| What factor changes the position of equilibrium? | Temperature |
| How does increasing the concentration of a reactant affect the position of equilibrium? | Changing the concentration changes the value of Q. The position of equilibrium will shift to make Q equal to K |
| How does increasing the pressure affect the position of equilibrium? | Changing the pressure will change the value of Q. The position of equilibrium will shift to make Q equal to K. |
| How does changing the temperature affect the equilibrium constant? | Altering the temperature causes more or less product to form, changing the value for Q. To reach equilibrium K changes to equal Q. |
| What is an acid? | Proton donator |
| What is a base? | Proton acceptor |
| What is a strong acid? | One which fully dissociates in water |
| What is a weak acid? | One which partially dissociates in water |
| What are conjugate pairs? | Species on opposite sides of a reaction that are linked by the transfer of a proton. The species that has lost a proton is the conjugate base and the species that has gained a proton is the conjugate acid. |
| What is the enthalpy of neutralisation? | The energy transferred when a solution of acid and base react together to produce one mole of water in standard conditions |
| Why does the enthalpy of neutralisation vary with weak acids and bases? | They dissociate partially in a reversible reaction, in which their ions are constantly used up so there is only a few of them in solution. The acid or base dissociates more to counteract this and maintain the equilibrium. This requires enthalpy, so there are enthalpy changes for both the forward and reverse reactions. The enthalpy of dissociatation varies, unlike the enthalpy of the reaction between H+ and OH-, so the enthalpy of neutralisation varies with different weak acids and bases. |
| Why is the enthalpy of neutralisation for strong acids and bases similar? | They fully dissociate in water, so there is no enthalpy for dissociation. This means the enthalpy of neutralisation is just the enthalpy of the reaction between H+ and OH-. This reaction is the same for all neutralisation reactions, so the value is always the same. |
| How would you find pH? | pH = -log[H+] |
| Define monoprotic | Each mole of acid produces one mole of hydrogen ions so the H+ concentration is equal to the concentration of acid. |
| What is a polyprotic acid? | Each mole of acid produces 2 or more moles of H+ ions so the H+ concentration is larger than the concentration of acid |
| What is the weak acid assumption? | [HA]start = [HA]equilibrium [H+] = [A-] This is represented by: [H+]^2 / [HA] |
| What is the expression for the ionic product of water? | Kw = [H+][OH-] |
| What is the value for Kw at 298K? | 1.0 x 10^-14mol^2dm^-6 |
| How would you find the pH of a strong base? | You know that [OH-] is equal to concentration of base. Use the value of Kw to calculate the [H+] and use that to find pH |
| How would you find pKa? | -logKa |
| How does diluting strong acid affect it's pH? | Diluting increases volume, therefore decreases concentration of [H+]. pH = -log[H+] so decreasing by a factor of 10 will increase pH by 1 |
| How does dilution affect the pH of a weak acid? | Increasing volume decreases [H+] concentration. Ka = [H+]^2 / [Acid], so [H+] = √Ka[Acid] pH = -log[H+] , so if [H+] decreases by a factor of 10, the pH increases by 0.5 |
| Describe the shape of a titration curve | The initial pH is the pH of the acid or base you start with. The pH does not change initially, at equivalence point the pH suddenly changes to form a vertical line. The final pH is the pH of the acid or base added. For strong acid - weak base the line at the equivalence point is vertical, more sloped with weak acid - strong base or strong acid - weak base and even more sloped for weak acid -weak base. |
| What is the equivalence point | The point where [H+] = [OH-] |
| What would be a suitable indicator for a titration knowing the range for the indicator and the pH of the acid and base titrated? | One which has a range within the vertical range |
| How do you find pKa on a titration curve? | At half equivalence point half the acid is neutralised, so [HA] = [A-]. Ka = [H+][A-] / [HA], the [A-] and [HA] are cancelled out, so Ka = [H+] Log this to make pKa = pH |
| What is a buffer? | A solution that resists a change in pH when small amounts of acid and base are added. |
| What is an acidic buffer? | One which contains a weak acid and it's conjugate base, which can be done by either mixing a weak acid and the salt of the conjugate base or an excess of weak acid with a strong base |
| What is an alkaline buffer? | One which contains a weak base and one of it's salts |
| Describe the shape of titration curve of a buffer and a strong base | The pH changes quickly initially as the base increases the concentration of OH- and the pH increases. Then the curve levels off as the buffer H+ ions react with the OH- to bring the position of equilibrium back to normal. Then the graph looks similar to a regular titration curve, with a vertical range and then levels off as the OH- concentration becomes to large to counteract |
| Describe how the blood acts as a buffer | The buffer in the blood contains carbonic acid and hydrogencarbonate ions. If [H+] increases, HCO3- ions react with them to shift the position of equilibrium back to normal. If [H+] falls, carbonic acid dissociates to form more H+ ions. H2CO2 <--> H+ + HCO3- |
| What assumptions are made when calculating the pH of an acidic buffer solution? | The salt of the conjugate base is fully dissociated so [A-] = initial concentration of salt HA is only slightly dissociated, so its equilibrium concentration is the same as its initial concentration |
| How do you calculate the pH of a buffer? | Write the expression for Ka of the weak acid, then rearrange to make [H+] the subject. Calculate [H+], then -log it to get pH. |
| Give the Henderson-Hasselbalch equation | |
| What assumptions are made when using the Henderson-Hasselbalch equation? | [HA]equilibrium = [HA]start [A-]equilibrium = [A-]start |
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