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AQA Chemistry > Energetics > Flashcards

Energetics Flashcards

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1
Q

What is the definition of exothermic

A

Exothermic – a reaction that transfers energy to the surroundings so the temperature of the surroundings increases.

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2
Q

What is the definition of endothermic

A

Endothermic – a reaction that takes in energy from the surroundings so the temperature of the surroundings decreases.

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3
Q

What is the definition of activation energy

A

Activation energy - The minimum amount of energy that particles must have to react.

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4
Q

What is the definition of reaction profile

A

Reaction profile - used to show the relative energies of reactants and products, the activation energy and the overall energy change of a reaction.

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5
Q

What is the definition of reaction pathway

A

Reaction pathway – the line from the products to reactants on the reaction profile.

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6
Q

What is the definition of enthalpy

A

Enthalpy – A thermodynamic property of a system linked to the internal energy. Represented by H.

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7
Q

What is the definition of ΔH

A

ΔH – change in enthalpy. Negative for an exothermic reaction, positive for an endothermic reaction.

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8
Q

What is the definition of standard conditions

A

Standard conditions – 298K, 100kPa

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9
Q

What is the definition of standard enthalpy of reaction ΔrHθ

A

Standard enthalpy of reaction ΔrHθ – The enthalpy change when substances react under standard conditions given by the equation for the reaction.

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10
Q

What is the definition of standard enthalpy of formation ΔfHθ

A

Standard enthalpy of formation ΔfHθ – The enthalpy change when 1 mole of a compound is formed from its constituent elements with all reactants and products in standard states under standard conditions.

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11
Q

What is the definition of standard enthalpy of combustion

A

Standard enthalpy of combustion ΔcHθ – The enthalpy change when 1 mole of a substance is burned completely in excess oxygen with all reactants and products in their standard states under standard conditions.

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12
Q

What is the definition of Principle of conservation of energy

A

Principle of conservation of energy – Energy can not be created or destroyed, only changed from one form into another.

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13
Q

What is the definition of Hess Law

A

Hess Law – the enthalpy change for a chemical reaction is independent of the route taken and depends only o the initial and final states.

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14
Q

What is the definition of mean bond energy

A

Mean bond energy – the energy required to break one mole of covalent bonds in the gaseous state averaged across many compounds containing the bond.

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15
Q

What is the calculation to work out enthalpy change from an experiment?

A

Energy change = mass x specific heat capacity x temperature change q=mcΔT m = mass in grams of the substance to which the temperature change occurs.

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16
Q

How does bond length affect the strength of the bond?

A

The shorter the covalent bond the stronger the bond.Triple bonds are shorter and stronger than double etc.Bond length increases down a group. (radius increases) Bond strength decreases. (except Fluorine – see Halogens KO)

17
Q

Why is calculated bond energy higher than experimental?

A

Uses mean bond values. In gaseous phase. Practical values will be lower due to heat loss to the environment.

18
Q

What happens in a chemical reaction in terms of energy?

A

During a chemical reaction: energy must be supplied to break bonds in the reactants energy is released when bonds in the products are formed.

19
Q

How can the overall energy be calculated?

A

The energy needed to break bonds and the energy released when bonds are formed can be calculated from bond energies.

20
Q

What is the overall energy change in a reaction?

A

The difference between the sum of the energy needed to break bonds in the reactants and the sum of the energy released when bonds in the products are formed is the overall energy change of the reaction.

21
Q

Why do exothermic reactions give out heat?

A

In an exothermic reaction, the energy released from forming new bonds is greater than the energy needed to break existing bonds.

22
Q

Why do endothermic reactions take in heat?

A

In an endothermic reaction, the energy needed to break existing bonds is greater than the energy released from forming new bonds.

AQA Chemistry (13 decks)

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