zero order: - describe the conc-time graph a chemical with this order - how does changing the conc of a chemical of this order affect rate? - how does the half life on a conc-time graph change over time?

- linear graph, negative gradient - changing conc does not affect rate - half life decreases over time

first order: - describe the conc-time graph a chemical with this order - how does changing the conc of a chemical of this order affect rate? - how does the half life on a conc-time graph change over time?

- curved, negative gradient, starts steep and gets shallower - changing conc changed rate by the same factor - half life is constant

second order: - describe the conc-time graph a chemical with this order - how does changing the conc of a chemical of this order affect rate? - how does the half life on a conc-time graph change over time?

- just like first order graph but starts VERY steep - changing conc changes rate by the same factor squared - half life increases with time

5.1 rates, equilibrium and pH Flashcards by Sophia Amin

define rate of reaction

change of concentration of reactant or product per unit of time

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give the equation for overall rate of reaction

change in conc of reactant or product ÷ time

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what is order of a chemical?

order with respect to a chemical shows how changing concentration of the chemical affects rate of reaction

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what is overall order?

the orders of each reactant added up

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what is the rate determining step?

the slowest step in a chemical reaction

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zero order:

describe the conc-time graph a chemical with this order
how does changing the conc of a chemical of this order affect rate?
how does the half life on a conc-time graph change over time?

linear graph, negative gradient
changing conc does not affect rate
half life decreases over time

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first order:

describe the conc-time graph a chemical with this order
how does changing the conc of a chemical of this order affect rate?
how does the half life on a conc-time graph change over time?

curved, negative gradient, starts steep and gets shallower
changing conc changed rate by the same factor
half life is constant

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second order:

describe the conc-time graph a chemical with this order
how does changing the conc of a chemical of this order affect rate?
how does the half life on a conc-time graph change over time?

just like first order graph but starts VERY steep
changing conc changes rate by the same factor squared
half life increases with time

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what would be the rate equation of

A + B → C

rate = k[A]ˣ[B]ʸ

where x and y are the orders of reactants A and B

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how do you find the rate constant and its units?

work out order of all reactants
substitute in known values of the rate and concentrations of reactants
rearrange to find k
units are derived from units of rate and concentrations to the power of their orders

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describe the rate-concentration graph of a zero order chemical

horizontal line

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describe the rate-concentration graph of a first order chemical

linear
starting at origin
positive gradient

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describe the rate-concentration graph of a second order chemical

exponential
starting at origin
positive gradient

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how do you find the rate constant from a first order rate-concentration graph?

k = gradient

ONLY for first order

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how do you find the rate constant from a first order concentration-time graph?

k = ln2 ÷ half life

ONLY for first order

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what are two rules regarding order, rate equations and the rate determining step?

if a chemical is NOT in the rate equation it is NOT in the RDS.
the order of a chemical = the number of molecules in the RDS.

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in reaction mechanisms, what are intermediates?

species formed that do not appear in final equation, they are catalysts

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give the 2 equations of the arrhenius equation

name each variable and give the units

k = Ae^-Ea/RT
lnk = -Ea/RT  +  lnA

k = rate constant (units to be determined)
A = pre-exponential factor (same units as k)
Ea = activation energy (Jmol-1)
R = gas constant 8.314 (JK-1mol-1)
T = temp in KELVIN

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what can the arrhenius equation be approximated to? what do each part of the arrhenius equation represent in the approximation?

equation of straight line - y = mx + c
y = lnk
m = -Ea/R
x = 1/T
c = lnA

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plotting arrhenius equation:

what goes on the x and y axis?

y axis = lnk

x axis = 1/T

plotting arrhenius equation

how do you find Ea from the graph?

find gradient of the line of best fit using a triangle
multiply gradient by gas constant 8.314 to find Ea in Jmol-1
divide by 1000 to find it in kJmol-1

plotting arrhenius equation

how do you find A or the pre-exponential factor from the graph?

extrapolate backwards to the y axis and find the y intercept
lnA = y intercept so put this number to the power of e
OR
once you have found the Ea, substitute data from the table into either of the equations
rearrange to find A

what is a homogenous system?

a reaction where all reactants and products are the same state

what is a heterogenous system?

a reaction where more than one state of matter is present in reactants and products

in the equation: aA + bB ⇋ cC + dD what is the Kc equation?

Kc =[C]^c[D]^d / [A]^a[B]^b | product conc / reactants conc

what states of matter are included in the Kc equation?

only aqueous and gases concentrations are included

how do you find the moles/concentration of substances in equilibrium from a reaction?

using RICE tables: R - reaction and molar ratios go here I - initial moles of reactants and initial mol of products = 0 C - change of moles: changes with molar ratios: opposite operation happens to products and reactions (eg. if change is +ve for reactants its -ve for products) E - equilibrium moles in this row

what does the equilibrium constant, Kc, indicate?

the position of equilibrium

where is the position of equilibrium when: 1. Kc = 1 ? 2. Kc < 1 ? 3. Kc > 1 ? 4. Kc << 1 ? 5. Kc >> 1 ?

1. in the middle of products and reactants 2. favours reactants 3. favours products 4. lies far to the left 5. lies far to the right

what is the only factor that affects the equilibrium constant?

temperature

what effect does increasing/decreasing temperature do to position of equilibrium?

increasing - to endothermic direction | decreasing - to exothermic direction

what happens to Kc when you change concentration or pressure? why?

Kc doesn't change because the system works to restore Kc to it's original value

what is Kp

same constant as Kc but instead of concentration, partial pressure of gases are used

define mole fraction and give the equation

proportion of given substance present in the reaction mixture mole fraction = moles of compound/total moles of products and reactants

define partial pressure and give the equation

the pressure exerted by an individual gas if it occupied the whole vessel on its own partial pressure = mole fraction x total pressure

give the equation of Kp given the reaction aA + bB ⇋ cC + dD what must you use in the equation?

partial pressure of each gas raised to the power of their stoichiometry Kp = (Pc)^c (PD)^d / (PA)^a (PB)^b must use ROUND brackets

how do you find the value of Kp?

use a rice table but add rows M (mole fraction) and P (partial pressure)

give the bronsted lowry (BL) definitions of an acid and base

acid - proton donor (loses H+) | base - proton acceptor (gains H+)

what are three names given to acids? what do these names refer to?

monobasic/protic dibasic/protic tribasic/protic names refer to how many H+ ions the acid loses

what is a conjugated acid and base pair?

two species that can transform into each other by loss or gain of H+ ions

in this reaction NH₃ + HCl ⇋ NH₄⁺ + Cl⁻ what are the conjugated acid-base pairs?

NH₃ is the BL base and NH₄⁺ is the conjugate acid because it can LOSE a H+ ion to become NH₃ HCl is the BL acid and Cl⁻ is the conjugate base because it can GAIN a H+ ion to become HCl

how do you find the concentration of H+ ions when given the pH?

[H⁺] = 10 ^-pH | 10 to the power of -pH

how do you find pH of a solution when given the concentration of H⁺ ions?

pH = -log[H⁺] | negative log of the conc of H+ ions

pH increases = [H⁺] ions _______

decreases

pH decreases = [H⁺] ions _______

increases

what is assumed about the concentration of a strong acid?

in this strong acid HA ---> H⁺ + A- | [HA] = [H⁺] is assumed because we assume all H+ ions completely disassociate

derive the equation involving the equilibrium constant for acids

HA ---> H⁺ + A- Ka = [H⁺][A-] / [HA] [H⁺] = [A-] so numerator can be written as [H⁺]² multiply by [HA] and square root to get [H⁺] = √(Ka[HA])

how do you find the pKa value?

``` pKa = -log(Ka) Ka = 10^-pKa ```

what does Kw symbolise?

- Kw is the equilibrium constant for the dissociation water - the ionic product of water - Kw = [H⁺][OH-]] - Kw = 1x10^-14