2.1 Thermochemistry Flashcards

1
Q

Exothermic reaction

A

Is a reaction that releases energy to the surroundings (creates a temperature increase) and the ΔH is negative

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2
Q

Endothermic reaction

A

Is a reaction that takes in energy from the surroundings (creates a temperature drop) and the ΔH is positive

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3
Q

Enthalpy

A

The heat content of a system at constant pressure

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4
Q

Enthalpy change

A

The heat added to a system at constant pressure

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5
Q

Chemical system is made up of the … and the …

A

Reactants
Products

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6
Q

What are the units for Enthalpy

A

Joules (J) or Kilojoules (kJ)

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7
Q

ΔH = … - …

A

Hproducts
Hreactants

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8
Q

For exothermic reactions Hproducts … Hreactants

A

Hproducts < Hreactants

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9
Q

For endothermic reactions Hproducts … Hreactants

A

Hproducts > Hreactants

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10
Q

Principle of conservation of energy

A

Energy cannot be created or destroyed only changed from one form to another

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11
Q

Standard conditions for temperature is …

A

298K or 25°C

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12
Q

Standard conditions for pressure is …

A

1 atm or 101,000Pa

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13
Q

What is the standard state of a substance

A

the substance in its pure form at 1atm and the stated temperature (normally 298K)

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14
Q

What is the symbol for standard enthalpy change

A

ΔHθ

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15
Q

What is the symbol for standard enthalpy change of formation

A

ΔfHθ

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16
Q

Enthalpy change of formation

A

Is the enthalpy change when one mole of a substance is formed from its constituent elements in their standard states under standard conditions.

17
Q

The “per mole” refers to the formation of one mole of … or the product

A

compound

18
Q

What are the units for ΔfHθ

A

kJmol-1

19
Q

What is the symbol for standard enthalpy change of combustion

A

ΔcHθ

20
Q

Enthalpy change of combustion

A

Is the enthalpy change when one mole of a substance is completely combusted in oxygen under standard conditions.

21
Q

The “per mole” refers to the … being combusted not the quantity of products formed

A

substance

22
Q

What is the symbol of Enthalpy change of reaction

A

ΔrH

23
Q

Enthalpy change of reaction

A

Is the enthalpy change in a reaction between the number of moles of reactants shown in the equation for the reaction.

24
Q

ΔrHθ = …(products) - ΣΔfH(reactants)

A

ΣΔfH

25
Q

Hess’s law

A

The total enthalpy change for a reaction is independent of the route taken from the reactants to the products.

26
Q

ΔH1 = ΔH + ΔH

A
  1. 2
  2. 3
27
Q

When using enthalpy changes of combustion use:
ΔcH = ΣΔcH(…) - ΣΔcH(…)

A
  1. reactants
    2.products
28
Q

When using enthalpy changes of formation use:
ΔfH = ΣΔfH(…) - ΣΔfH(…)

A
  1. products
  2. reactants
29
Q

Bond enthalpy

A

Is the enthalpy required to break a covalent X - Y bond into atoms X and Y, all in the gas phase

30
Q

Average bond enthalpy

A

Is the average value of the enthalpy required to break a given type of covalent bond in the molecules of a gaseous species

31
Q

q = mcΔT

A

q = the amount of heat transferred
m = the mass of the solution
c = the specific heat capacity of the solution
ΔT = the temperature change

32
Q

What is the specific heat capacity of water?

A

4.18Jg-1K-1