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chemistry > reactivity 1.1 > Flashcards

reactivity 1.1 Flashcards

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1
Q

temperature is the measure of _____

A

the average kinetic energy of the particles

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2
Q

heat is the measure of _____

A

the energy content of a substance

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3
Q

energy is a measure of ______

A

the ability to do work

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4
Q

what can/can’t open systems transfer? x2

A

can transfer energy AND matter

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5
Q

what can/can’t closed systems transfer? x2

A

can transfer energy BUT not matter

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6
Q

what can/can’t isolated systems transfer? x2

A

can not transfer energy NOR matter

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7
Q

inside the reaction vessel is known as ___

A

the system

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8
Q

outside the reaction vessel is known as ___

A

the surroundings

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9
Q

what does the law of conservation of energy state?

A

that energy is neither created or destroyed so the total energy of a process remains the same

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10
Q

define enthalpy

A

the chemical potential energy of a system/the measurement of energy in a thermodynamic system

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11
Q

when does enthalpy change?

A

when chemical reactions take place, changes in chemical energy take place

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12
Q

what symbol is an enthalpy change is represented by?

A

ΔH

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13
Q

an enthalpy change can be _______ or _________

A

positive or negative

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14
Q

what makes a reaction exothermic?

A

when the products have less enthalpy than the reactants

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15
Q

how does temperature in exothermic reactions change in surroundings/system?

A

heat energy is given off by the system to the surroundings (surroundings temp ↑, system temp ↓)

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16
Q

ΔH value in exothermic reactions

A

negative (because there is an enthalpy decrease)

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17
Q

why are exothermic reactions thermodynamically possible?

A

because Hreactants > Hproducts)

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18
Q

if the rate of the an exothermic reaction is too slow, what will happen?

A

the reaction may not occur, so the reaction becomes kinetically controlled

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19
Q

what makes a reaction endothermic?

A

when the products have more enthalpy than the reactants

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20
Q

how does temperature in endothermic reactions change in surroundings/system?

A

heat energy is absorbed by the system from the surroundings (surroundings temp ↓, system temp ↑)

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21
Q

ΔH value in endothermic reactions

A

positive (because there is an enthalpy increase)

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22
Q

“the substances that are reacting” is called ______

A

the system

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23
Q

what does an energy profile show? x3

A

energies of reactants, transition state(s) AND products of the reaction with time

24
Q

define transition state

A

a stage during the reaction at which chemical bonds are partially broken and formed

25
Q

is the transition state stable? why or why not?

A

no, it cannot be isolated and is higher in energy than reactants & products

26
Q

define activation energy (Eₐ)

A

‘the minimum amount of energy needed for reactant molecules to have a successful collision and start the reaction’ (the energy needed to reach the transition state)

27
Q

between exo and endo thermic reactions, which has a lower activation energy? why?

A

exothermic because the reactants are closer in energy to the transition state

28
Q

how to determine Eₐ from a drawn energy profile

A

the energy difference from the energy level of the reactants to the top of the ‘hump’

29
Q

what does the standard enthalpy change for a chemical reaction (ΔH^Ꝋ) refer to?

A

the heat transferred at constant pressure under standard conditions and states

30
Q

what are the standard conditions for ΔH^Ꝋ x3

A

pressure = 100 kPa, concentration = 1 mol dm⁻³ (for all solutions) AND each substance is in its standard state (gas/liquid/solid)

31
Q

what is the commonly given temperature for ΔH^Ꝋ?

A

298 K (25℃)

32
Q

what does Ꝋ signify?

A

that a reaction has been carried out under standard conditions

33
Q

define standard enthalpy change of reaction (ΔH^Ꝋᵣ), is it for both exo and endothermic reactions?

A

the enthalpy change when the reactants in the stoichiometric equation react to give the products under standard conditions (BOTH ENDO & EXO)

34
Q

define standard enthalpy change of formation (ΔH^Ꝋf), is it for both exo and endothermic reactions?

A

the enthalpy change when one mole of a compound is formed from its elements under standard conditions (BOTH ENDO & EXO)

35
Q

define standard enthalpy change of combustion (ΔH^Ꝋc), is it for both exo and endothermic reactions?

A

the enthalpy change when one mole of a substance is burnt in excess oxygen under standard conditions (ONLY EXO)

36
Q

define standard enthalpy change of neutralisation (ΔH^Ꝋneut), is it for both exo and endothermic reactions?

A

the enthalpy change when one mole of water is
formed by reacting an acid and alkali under standard conditions (ONLY EXO)

37
Q

define calorimetry

A

a technique used to measure changes in enthalpy of chemical reactions

38
Q

examples of what can a calorimeter be made of x3

A

polystyrene drinking cup, vacuum flask OR metal can

39
Q

define specific heat capacity (c) (of the liquid)

A

the energy needed to raise the temperature of 1g of a substance by 1K

40
Q

what is the specific heat capacity of water?

A

4.18 J g⁻¹ K⁻¹

41
Q

how can energy transferred as heat be calculated? what do each of the letters mean & what are their units? x2

A

q = m∙c∙ΔT
q ⇒ heat transferred (J)
m ⇒ mass of water (g)
c ⇒ specific heat capacity (J g⁻¹ K⁻¹)
ΔT ⇒ temperature change (K)

ΔH = - Q / n
ΔH ⇒ change in enthalpy (kJ mol⁻¹)
q ⇒ heat transferred (J)
n ⇒ # of moles (mol)

42
Q

two types of calorimetry experiments

A

enthalpy changes of reactions in a solution AND enthalpy changes of combustion

43
Q

principle of ΔH for reactions in solution

A

the principle of these calorimetry experiments is to carry out the reaction with an excess of one reagent and measure the temperature change over the course of a few minutes

44
Q

define reagent

A

a substance or compound added to a system to cause a chemical reaction

45
Q

what assumptions are made for ΔH for reactions in solution? 5

A

c of the solution is = pure water (4.18 J g⁻¹ K⁻¹), density of solutions = pure water (1g cm⁻³), c is ignored, reaction is complete AND there are negligible heat losses

46
Q

what are temperature correction graphs used for?

A

for reactions which are not instantaneous, there may be a delay before the maximum temperature is reached

47
Q

for non-instantaneous reactions, why may the true maximum temperature not be reached?

A

during the delay substances may be losing heat to surroundings

48
Q

steps to making a temperature correction graph x3

A
  1. take temperature reading before adding reactants to get a steady value
  2. add second reactant and continue recording temperature & time
  3. plot the graph and extend the cooling part of the graph until you intersect the time where the second reactant was added
49
Q

principle of ΔH of combustion experiments

A

the principle here is to use the heat released by a combustion reaction to increase the heat content of water

50
Q

components of a typical & simple calorimeter used to measure the temperature changes to the water (in an ΔH of combustion experiment) x6

A

insulating lid, water, copper cam, thermometer, draught/draft shield AND spirit burner

51
Q

where can some of the heat produced by the ΔH of combustion reaction escape to (not being transferred to the water)? x2

A

surroundings AND absorbed by calorimeter

52
Q

ways to minimize heat losses in a calorimeter measuring temperature changes to the water (ΔH of combustion) x3

A

copper calorimeter should not be too far above the flame, lid placed overtop AND draught/draft shields to block any air currents

53
Q

main sources of error in ΔH of combustion calorimeter experiments x2

A

heat losses AND incomplete combustion

54
Q

how is water contained in experiments to determine H changes in solution?

A

in an insulated calorimeter

55
Q

what does a thermochemical equation give?

A

the equation for the reaction and the corresponding enthalpy change

chemistry (8 decks)

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