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Chem module 3 > Enthalpy changes > Flashcards

Enthalpy changes Flashcards

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1
Q

Law of conservation of energy?

A

Energy cannot be created or destroyed, only transferred

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2
Q

Enthalpy?

A

Measure of heat energy present in a system

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3
Q

What letter represents enthalpy

A

H

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4
Q

Enthalpy change?

A

Energy released or taken in during a chemical reaction

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5
Q

Exothermic reaction?

A

Reaction which releases energy to the surroundings

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6
Q

Is the enthalpy change value for an exothermic reaction pos or neg

A

Neg

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7
Q

Endothermic reaction?

A

Reaction which takes in energy from the surroundings

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8
Q

Is the enthalpy change value of an endothermic reaction pos or neg

A

Positive

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9
Q

Activation energy?

A

Minimum energy requires for a reaction to take place

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10
Q

Symbol for activation energy

A

E subscript a

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11
Q

Why are standard conditions relevant to enthalpy changes

A

The enthalpy change of a reaction can vary depending on the conditions provided

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12
Q

What are the standard condition? 4

A

100kPa (approx 1atm pressure)
298 K (25°c)
1 mol dm^-3 (relevant for sols)
Standard state

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13
Q

what is standard state

A

The state of a substance under standard conditions e.g H2O is liquid

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14
Q

Is RTP the same as standard conditions

A

No

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15
Q

Symbol for standard conditions

A

circle with a line through

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16
Q

Definition for standard enthalpy change of reaction? 3 parts

A

The enthalpy change associated with a stated equation in the molar quantities shown in the chemical equation under standard conditions

17
Q

units for enthalpy change

A

kJ mol^-1

18
Q

Definition for standard enthalpy change of formation 2parts

A

The enthalpy change associated with the formation of one mole of a compound from its elements under standard conditions

19
Q

What is the enthalpy change of formation for an element

A

Zero

20
Q

Definition for standard enthalpy change of combustion

A

The enthalpy change associated with the complete combustion of one mole of a substance under standard conditions

21
Q

Definition for standard enthalpy change of neutralisation 3 parts

A

The enthalpy change associated with the formation of one mole of water from a naturalisation reaction between an acid and a base, under standard conditions

22
Q

What iss the value of the enthalpy change of neutralisation for the reaction between a strong acid and base

A

-57 km mol^-1

23
Q

Is standard enthalpy change of combustion always pos or neg, why?

A

Always neg bc combustion is an exothermic reaction

24
Q

Why is standard enthalpy change of neutralisation normaly the same value across different reactions?

A

Bc the same half equation is maintained: one mol of H+, one mol of OH- to form one mol oh H2O

25
Q

Subscript of standard enthalpy change of neutralisation

A

neut

26
Q

subscript of standard enthalpy change of combustion

A

c

27
Q

subscript of standard enthalpy change of formation

A

f

28
Q

subscript of standard enthalpy change of reaction

A

r

29
Q

symbol for heat energy (Not enthalpy)

A

q

30
Q

equation for calculating heat energy transferred between a system and its surroundings

A

q=mc delta T

31
Q

unit for specific heat capacity (c)

A

J g^-1 K^-1

32
Q

Unit for temp

A

Kelvin

33
Q

how can we more accurately calculate change in temp experimentally

A

with a cooling curve extrapolation

34
Q

Hiw do you produce a cooling curve extrapolation

A

Take temp of sol at short, regular intervals
Add other reactant to sol
Record temp of reaction mixture at regular intervals
Plot a cooling curve
Extrapolate the line of best fit and draw a line up from the x axis front he time the reactants were added to the sol
The crossing point of the 2 lines is the max temp

35
Q

what is the function of a cooling curve extrapolation

A

corrects for heat loss during the experiment

Chem module 3 (6 decks)

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