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IB Chemistry > Topic 5.1: Measuring energy changes > Flashcards

Topic 5.1: Measuring energy changes Flashcards

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1
Q

Definition of heat

A

A form of energy that flows from a body at high temperature to a body at a low temperature

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2
Q

Definition of temperature

A

A measure of the average kinetic energy of particles in a substance

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3
Q

Definition of internal energy

A

Total amount of energy in a sample of a substance

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4
Q

Definition of system

A

Part of the universe chosen for study

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5
Q

Types of system

A

a) Open
b) Closed
c) Isolated

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6
Q

Definition of surroundings

A

Part of the universe outside the system which the system interacts with

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7
Q

First law of thermodynamics (Law of conservation of energy)

A

Energy can be converted from one form to another, but it is neither created nor destroyed

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8
Q

Definition of enthalpy

A

Internal energy contained in a substance

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9
Q

Definition of enthalpy change (units)

A

Amount of heat exchanged with the surroundings at constant pressure (kJ mol-1)

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10
Q

Can enthalpy be measured?

A

Enthalpy changes can be measured, no absolute values of enthalpy

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11
Q

Exothermic reactions

A

a) Heat is released to the surroundings
b) Enthalpy change has negative values
c) Products are more stable than reactants

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12
Q

Examples of exothermic reactions

A

a) Bond formation
b) Combustion
c) Gas => Liquid => Solid

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13
Q

Endothermic reactions

A

a) Heat is absorbed from the surroundings
b) Enthalpy change has positive values
c) Products are less stable than the reactants

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14
Q

Examples of endothermic reactions

A

a) Bond breaking
b) Solid => Liquid => Gas
c) Photosynthesis

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15
Q

Standard enthalpy change

A

Enthalpy change of a reaction carried out under standard conditions with everything in its standard state

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16
Q

Standard conditions

a) Pressure
b) Temperature
c) Molarity

A

a) 101.3 kPa
b) 298 K
c) 1 mol dm-3

17
Q

Standard enthalpy change of formation

A

Enthalpy change when one mole of substance in its standard state is formed from its elements in their standard states under standard conditions

18
Q

Formula to calculate enthalpy change from formation

A

Enthalpy change of reaction = Sum of the enthalpy of formation of products - Sum of the enthalpy of formation of reactants

19
Q

What is the value of the enthalpy of formation of elements in their standard state?

A

0

20
Q

Standard enthalpy of combustion

A

Enthalpy change when one mole of a substance in its standard state is burned completely in oxygen under standard conditions.

21
Q

Common products of combustion reactions

A

CO2 + H2O

22
Q

What type of reaction are combustion reactions?

A

Exothermic

23
Q

Formula to calculate enthalpy change from combustion

A

Enthalpy change of reaction = Sum of the enthalpy of combustion of reactants - Sum of the enthalpy of combustion of products

24
Q

Requirements of thermochemical equations

A

a) Value of enthalpy change
b) State symbols
c) Balanced equation

25
Q

Formula to calculate heat change from temperature change

A

q = mc∆T

26
Q

Specific heat capacity

A

Energy required to raise the temperature of 1g of a substance by 1K

27
Q

Formula to calculate enthalpy change

A

∆H = q / n

28
Q

Enthalpy change of neutralization

A

Enthalpy change when an acid and base react together to form one mole of water under standard conditions

29
Q

What type of reaction are neutralization reactions?

A

Exothermic

30
Q

Steps to calculate enthalpy change of neutralization

A

a) Calculate the number of moles of acid and base using n=cv
b) Determine the limiting reactant.
c) Add the volumes of acid and base together (where 1cm3 = 1g) to get the mass
d) Use Q=mc∆T to calculate enthalpy change
e) Use ∆H=Q / n where n is number of moles of water produced

31
Q

Assumptions at calculating enthalpy change of solutions

A

a) No heat loss from the system
b) All heat is transferred to water
c) The density of solutions are the same as water, so 1 cm3 of solution has 1 g.
d) The specific heat capacity of the mixture is the same as that of water.

32
Q

Definition of calorimetry

A

Process of measuring the amount of heat released or absorbed during a chemical reaction

33
Q

Assumption of calorimetry of combustion reactions

A

a) All heat is transferred to the water
b) Mass of water remained constant
c) Unlimited source of oxygen
d) Done under standard conditions

34
Q

Errors of calorimetry of combustion reactions

A

a) Incomplete combustion
b) No all heat transferred to water
c) loss of heat from water to surroundings
d) Mass and specific heat capacities of container taken into account
e) Incorrect recording of mass of substance burned due to evaporation

35
Q

How to compensate heat loss of water in a displacement reaction

A

Extrapolate the graph recorded

IB Chemistry (39 decks)

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