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Chemistry > Chapter 6: Thermochemistry > Flashcards

Chapter 6: Thermochemistry Flashcards

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1
Q

What is enthalpy (H)

A

A state function that is defined as:
H = E + PV
E: Internal energy of the system
P: Pressure of the system
V: Volume of the system

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2
Q

What is true about the change in enthalpy at constant pressure

A

ΔH = q p

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3
Q

What is the formula to calculate the enthalpy change in a chemical reaction?

A

/\H = Hproducts-Hreactants

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4
Q

What happends when:
1. /\H = Hproducts is greater than Hreactants
2. /\H = Hproducts is smaller than Hreactants

the sign, and what happends

A
  1. /\H is positive (Heat is absorbed by the system - reation is endothermic)
  2. /\H is negatve (overall decreased in enthalpy is achieved by the generation of heat - reation is exothermic)
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5
Q

What is calorimetry (the science of measuing heat) based on?

A

Based on observations of temperature change when a body absorbs or discharges energy in the form of heat

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6
Q

what is a calorimiter

A

Device used to determine the heat associated with a chemical reaction

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7
Q

What is the formula for heat capacity

A

C = heat absorbed / increase in temperature

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8
Q

What is specific heat capacity

A

Energy required to raise the temperature of one gram of a substance by one degree Celsius

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9
Q

What is molar heat capacity

A

Energy required to raise the temperature of one mole of a substance by one degree Celsius

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10
Q

What is notable about the conditions for constant pressure calometry (ie. a coffe cup calorimeter)

A

Atmospheric pressure remains constant during the process (*ΔH = q p )

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11
Q

in constant pressure calorimetry, when two reactants at the same temperature are mixed, what happends to the solution (exothermic vs endothermic)

A
  • An exothermic reaction warms the solution
  • An endothermic reaction cools the solution
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12
Q

What is the calculation of heat for a neutralization reaction

A

s x m x Δt

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13
Q

what does it mean to say that heat of a reation is an extensive product

A

it depends entirely on the amount of substance

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14
Q

When do you use constant-volume calorimetry

A

Used in conditions when experiments are to be performed under constant volume

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15
Q

is work done in constant volume calorimetry? Why or why not

A

No work is done since V must change for PV work to be performed

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16
Q

How does a bomb calorimeter function, and what kind of calorimeter is is?

A

(Constant volume calorimetry)
- Weighed reactants are placed within a rigid steel container and ignited
- Change in energy is determined by the increase in temperature of the water and other parts

17
Q

What is the formula for constant-volume calorimetry process

A

(ΔV = 0)
therefore, w = -PΔV = 0
ΔE = ΔT × heat capacity of the calorimeter

18
Q

Concerning Hess’s law, what do you need to keep in mind?

(2)

A
  1. If a reaction is reversed, the sign of ΔH is also reversed
  2. If the coefficients in a balanced reaction are multiplied by an integer, the value of ΔH is multiplied by the same integer
19
Q

What is the Standard Enthalpy of Formation (ΔHf)

A

Change in enthalpy that accompanies the formation of one mole of a compound from its elements with all substances in their standard states

20
Q

What is the standard state?

A

Precisely defined reference state

21
Q

What is the standard state for a gaseous substance?

A

Standard state for a gaseous substance is a pressure of exactly 1 atm

22
Q

What is the standard state for a pure substance?

A

the standard state is the pure liquid or solid

23
Q

What is the standard state for a substance in solution?

A

For a substance in solution, the standard state is a concentration of exactly 1M

24
Q

What is the Conventional Definitions of Standard States for an Element

A

Standard state of an element is the form in which that element exists under conditions of 1 atm and 25 C

ex. standard state of oxygen: O2(g)

25
Q

What is the ΔHf for an element in its standard state

A

zero

26
Q

How many pairs of electrons are shared in each type of bond
1. Single bond
2. Double bond
3. Tripple bond

A
  1. Single bond : One pair of electrons is shared
  2. Double bond : Two pairs of electrons are shared
  3. Triple bond : Three pairs of electrons are shared
27
Q

What happends to the bond length with the increse in number of shared electrons?

A

it shortens

Chemistry (7 decks)

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