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chemistry > 06 - enthalpy changes > Flashcards

06 - enthalpy changes Flashcards

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1
Q

exothermic reaction?

A

heat energy is released during a reaction, change in H = - ive

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2
Q

surroundings include:

A

. the solvent
. air around test tube
. test tube
. anything dipping in the test tube

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3
Q

examples of exothermic reactions:

A

. combustion of fuels
. oxidation of carbs in plant and animals bodies
. reaction of water with calcium oxide

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4
Q

endothermic reaction?

A

heat is absorbed during a reaction, value of change in H is +ive

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5
Q

examples of endothermic reactions?

A

. thermal decomposition reactions
. photosynthesis
. dissolving certain ammonium salts in water

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6
Q

what is enthalpy change?

A

the heat energy transferred during a chemical reaction

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7
Q

what is enthalpy change?

A

the heat energy transferred during a chemical reaction

unit = kJ mol-1
symbol = <> (delta)

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8
Q

what are reaction pathway diagrams?

A

shows the relative enthalpies of the reactants and products and rhe enthalpy change as an arrow, may include activation energy

x = reaction pathway
y = enthalpy change

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9
Q

what is activation energy?

A

the minimum energy that colliding particles must possess to break bonds to start a chemical reaction

always positive value of <>H

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10
Q

enthalpy change in reaction pathway diagrams

A

exo - arrow goes down
endo - arrow goes up

FROM REACTANTS TO PRODUCTS

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11
Q

activation energy in reaction pathways diagram

A

exo - arrow goes up
endo - arrow goes up

FROM REACTANTS TO PRODUCTS

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12
Q

what are standard conditions?

A

. 101 kPa pressure
. 298K temperature
. each substance involved in reaction is in its normal physical state (solid, liquid, gas)

symbol = circle with horizontal line between

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13
Q

what are the types of enthalpy changes?

A

. enthalpy change of formation
. enthalpy change of combustion
. enthalpy change of neutralisation
. enthalpy change of reaction

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14
Q

what is enthalpy change of reaction

A

the enthalpy change when the amount of reactants shown in the stoichiometric equation react to give products under standard conditions

EXO OR ENDO

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15
Q

what is enthalpy change of formation

A

the enthalpy change when one mole of compound is formed from its elements under standard conditions

EXO OR ENDO

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16
Q

enthalpy change of formation or any element in its standard state is

A

0

17
Q

what is enthalpy change of combustion?

A

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

ALWYAS EXO

18
Q

what is enthalpy change of neutralisation?

A

the enthalpy change when one mole of water is formed by the reaction of an acid with an alkali under standard condition

19
Q

when writing enthalpy changes, use most stable form of atoms

A
20
Q

what is the technique used to measure enthalpy chnage of some reaction

A

calorimetry

21
Q

what is the apparatus used in calorimetry?

A

calorimeter

22
Q

what is the apparatus used in calorimetry?

A

calorimeter

23
Q

what is specific heat capacity?

A

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

24
Q

q = mc<>T

A

q - heat transferred, J
m - mass of water, g
c - specific heat capacity, J g-1 °C - 1
T - temperature change in °C

25
Q

<>H = - mc<>T

A
26
Q

finding the enthalpy change of combustion

A

. weigh spirit burner
. pour 100cm3 water into calorimeter
. stir water and record temperature
. light spirit burner and remove the cap
. stir water with thermometer until a temperature rise of 10°C
.remove spirit burner and reweigh

27
Q

whta is hess’s law?

A

the enthalpy change ina chemicla reaction is independent of the route by which the chemical reaction takes place as long as the initial and final conditions and states of reactants and products are the same for route

28
Q

law of conservation of energy/ forst law of thermodynamics

A

energy cannot be created or destroyed

29
Q

direct route = indirect route

A

<>H2 = <>H1 + <>Hr

30
Q

enthalpy change reaction from formation

A

. elements at bottom
. arrows up

31
Q

enthalpy change formation from combustion

A

. combustion products at bottom
. arrows down

32
Q

bond break energy > bond make

A

endo

33
Q

bond break energy < bond make

A

exo

34
Q

what is exact bond energy

A

energy needed to break a specific covalent bond in a named molecule in the gaseous state

AKA. bond dissociation energy, bond enthalpy

35
Q

what is average bond energy?

A

the average energy needed to break a specific covalent bond averaged from a variety of molecules in the gaseous state

36
Q

what is standard enthalpy change of atomisation?

A

when one mole of gaseous atoms is formed from its element under its standard conditions

chemistry (18 decks)

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