Topic 8 Enthalpy Changes Flashcards

1
Q

Exothermic

A

-(delta)H
increase in temperature

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2
Q

Endothermic

A

+(delta)H
decrease in temperature

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3
Q

What is thermochemistry?

A

The study of energy changes in chemistry.

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4
Q

System

A

Just the material or mixture of chemicals being studied.

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5
Q

Surroundings

A

Everything around the system (eg. apparatus or air in the lab).

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6
Q

Closed system

A

System can’t exchange matter with the surroundings because the reaction flask is closed with a bung. Energy can’t be transferred.

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7
Q

Open system

A

A material system in which mass or energy can be lost to or gained from the surroundings.

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8
Q

Examples exothermic reactions

A

-Combustion reactions
-Neutralisation reactions
-Displacement reactions

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9
Q

The standard enthalpy change of combustion

A

The enthalpy change when 1 mole of a substance is burned completely in oxygen under standard conditions (100kPa, 298K, 1atm).
forms CO2 + H2O when reacts with O2

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10
Q

What is the formula for specific heat capacity?

A

q=mcΔT
q=energy transferred (J)
m=mass of substance (kg)
c=specific heat capacity
ΔT=temperature change (K or °C)

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11
Q

The standard enthalpy change of neutralisation

A

When one mole of water is produced by the neutralisation of an acid with an alkali.
The enthalpy change measured at 100kPa and a specific temperature, usually 289K.

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12
Q

The standard enthalpy of formation

A

When one mole of a substance is formed from its elements in their standard states.
The enthalpy change measured at 100kPa and a specific temperature, usually 298K.

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13
Q

Hess’s law

A

The enthalpy change of a reaction is independent of the route taken in converting the reactants into products provided the initial and final conditions are the same in each case.

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14
Q

Enthalpy cycle of combustion

A

+-

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15
Q

Bond enthalpy (basic definition)

A

The amount of energy needed to break bonds.

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16
Q

Making bonds

A

Negative

17
Q

Breaking bonds

A

Positive

18
Q

enthlapy change calc

A

broken - made
broken = seperate
made = together
separate - together

19
Q

better at keeping warm

A

better heat conductor

20
Q

why is catalyst warmed

A

to provide the activation energy
if the reaction is exothermic enough to melt the catalyst

21
Q

heterogenous catalyst

A

reactants absorb onto the catalyst
active sites on the catalyst
bonds in reactants weakened
products deabsorb from catalyst

22
Q

difference between bond enthalpy in table and actual

A

mean in a table rather than the actual values of molecules
standard conditions is in gas form so if liquid it will differ

23
Q

single bonds

A

2 sigma bonds

24
Q

double bonds

A

pi and sigma bonds
weaker than two single bonds

25
Q

enthalpy change in q=mct

A

mass formed / no of moles