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chemistry gsp > 3.1.4 energetics > Flashcards

3.1.4 energetics Flashcards

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1
Q

is bond breaking an exothermic or endothermic process?

A

Endothermic

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2
Q

is bond making an exothermic or endothermic process?

A

exothermic

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3
Q

What is the enthalpy change?

A

The heat energy change at constant pressure

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4
Q

What is the symbol for enthalpy change?

A

Delta H

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5
Q

what are the units of enthalpy change?

A

KJmol-1

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6
Q

what are the standard values of temperature and pressure?

A

Temperature: 298K (25°C)

Pressure: 100kPa

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7
Q

what is the standard enthalpy change at a temperature of 298K and a pressure of 100kPa?

A

Delta H 298

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8
Q

when is the reaction said to be exothermic?

A

If more energy is released when new bonds are formed

than was needed to break the bonds in the reactants

Then the difference in energy is released to the surroundings, and the reaction said to be exothermic

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9
Q

As energy is lost by the system to the surroundings, the sign of enthalpy change of the system is what?

A

negative

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10
Q

What does the energy level diagram for an exothermic reaction look like?

A
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11
Q

when is a reaction said to be endothermic?

A

If more energy is needed to break the bonds in the reactants

than was released when new bonds are formed

Then the difference in energy is absorbed from the surroundings

and the reaction is said to be endothermic

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12
Q

as energy is gained by the system from the surroundings, the sign of the enthalpy change of the system is what?

A

positive

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13
Q

what does the energy level diagram for an endothermic reaction look like?

A
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14
Q

do strong bonds need more or less energy to break?

A

More

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15
Q

definition: bond enthalpy

A

The enthalpy change when a covalent bond is broken, so the values are always positive

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16
Q

definition: mean bond enthalpy

A

The average enthalpy change when a specific bond is broken in a range of compounds

17
Q

what I mean bond enthalpies used to calculate?

A

The enthalpy change

18
Q

Definition: bond dissociation energy

A

The energy needed to break a particular covalent bond

19
Q

definition: standard enthalpy change of formation

A

The enthalpy change when one mole of a compound is formed from its elements with all reactants and products in their standard states and under standard conditions

20
Q

definition: standard enthalpy change of combustion

A

The enthalpy change when one mole of a substance is completely burned in excess oxygen with all reactants and products in their standard states and under standard conditions

Combustion reactions are always exothermic

21
Q

definition: standard enthalpy change of reaction

A

The enthalpy change when a reaction occurs in the molar quantity shown in the chemical equation, under standard conditions, with all reactants and products and their standard states

22
Q

The standard enthalpy of formation of an element must be what?

A

zero

23
Q

can the same reaction represent more than one type of reaction?

A

Yes

24
Q

what’s Hesses law also known as?

A

The first law of thermodynamics

25
Q

what does the first law of thermodynamics state?

A

Energy cannot be made or destroyed, but it can be converted from one form to another

26
Q

what does Hesses law state?

A

The total enthalpy change for a reaction is independent of the route taken

27
Q

A=

A

C-B

28
Q

extra info

A
29
Q

What is the equation for enthalpy change?

A

q=mc delta T

30
Q

Hey, what’s the number for specific heat capacity?

A

4.18

31
Q

How does a simple colorimeter work?

A
  • a spirit burner containing a liquid fuel is weighed
  • The spirit burner is placed beneath a copper can (colorimeter) containing a known volume of water (at a known temperature) and then lit
  • The water is stirred at regular intervals
  • When the temperature of the water has risen by at least 10°C, the flame is put out on the spirit burner is reweighed
  • Using the massive fuel used and the temperature rise of the water, the amount of heat energy released per gram of fuel can be calculated
32
Q

is a bomb colorimeter or a simple calorimeter more accurate, why?

A

A bomb calorimeter is more accurate

this is because the heat loss to the surroundings is reduced to 0

33
Q

What is calorimetry use to find?

A

The enthalpy changes for a reaction taking place in the solution

34
Q

in an exothermic reaction, heat is ………….. on the temperature of the water in the solution …………..

A

Released

Increases

35
Q

in an endothermic reaction, the heat energy …………. comes from the water in the solution, and the temperature of the solution ……………

A

Absorbed

Decreases

36
Q

how do you make this experiment more accurate?

A
  • Using a polystyrene cup and a beaker provides some insulation and placing a lid on top of the cup reduces heat loss

chemistry gsp (12 decks)

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