Section 9 chemical energy Flashcards

1
Q

Enthalpy definition

A

The measure of chemical energy stored in a substance .

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2
Q

What is enthalpy measured in

A

KJ mol-1

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3
Q

Exothermic reactions definition

A

A reaction where the products have a lower enthalpy and potential energy than reactants, meaning heat energy is released by the reaction.

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4
Q

Endothermic reaction definition

A

A reaction where the products have a higher enthalpy and potential energy than reactants, meaning heat energy is absorbed.

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5
Q

Industrial cost of exothermic reactions

A

Heat energy must be removed, since if temperature rises far too quickly there may be an explosion.

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6
Q

Industrial cost of endothermic reactions

A

Heat energy may be needed to be constantly supplied to keep the reaction occurring.

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7
Q

Heat energy equation

A

Eh = cm delta T

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8
Q

Specific heat capacity of water

A

4.18 KJ kg-1C-1

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9
Q

What is measured in an energy change experiment

A

Temperature change and mass of water.

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10
Q

How do you calculate the enthalpy of combustion

A

Eh = cm delta T
N = m/gfm
Eh/n

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11
Q

Enthalpy of combustion definition

A

The enthalpy change when one mole of a substance completely burns in oxygen.

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12
Q

Ways to minimise error in enthalpy of combustion experiment

A

Copper can to ensure heat energy is conducted.
Heat shield to prevent heat loss into environment.

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13
Q

Equations of enthalpy of combustion key characteristics

A

The substance burned in the reaction must be one mole.

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14
Q

Examples of equations of enthalpies of combustion

A

H2 +1/2O2 —> H2O
C + O2 —-> CO2

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15
Q

Hess’s law explanation

A

The enthalpy change for a reaction depends on the reactants and products, not on the route taken.

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16
Q

Hess’s law equations

A

Manipulate all target equations, to get reactants on their own, then add the enthalpy change of the reactions together.

17
Q

Why are Hess’s law equations used

A

To calculate the enthalpy change for reactions that can’t be carried out.

18
Q

Molar bond enthalpy

A

The energy required to break one mole of bonds in one mole of a diatomic molecule.

19
Q

Mean molar bond enthalpy

A

The average energy required to break one mole of bonds in one mole of a molecule, for a bond that occurs in a number of compounds.

20
Q

Enthalpy change of a reaction break down

A

Breaking bonds is endothermic and requires for energy to be absorbed.
Forming new bonds is exothermic and releases energy.

21
Q

What state must the substances be in to do a bond enthalpy.

A

Gas

22
Q

Bond enthalpy equation

A

Add the enthalpy of the bonds on the left side, take away the bonds on the right side.