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Inorganic Chem AS level > bond enthalpy > Flashcards

bond enthalpy Flashcards

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1
Q

what is enthalpy

A

H is a measure of the heat energy in a chemical system

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2
Q

what is a chemical system

A

refers to atoms molecules or ions making up a chemical reaction

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3
Q

what is enthalpy change

A

enthalpy change = Hproduct - H reactant

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4
Q

whats the law of conservation of energy

A

energy cannot be created or destroyed

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5
Q

what is the system

A

the chemicals,reactants,products

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6
Q

what is the surrounding

A

apparatus everything is not in the chemical system

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7
Q

what is the universe

A

everything contains both system and surrounding

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8
Q

what type of energy transfer is exothermic

A

system to surrounding

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9
Q

what type of energy transfer is endothermic

A

surrounding to system

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10
Q

what happens in exothermic reactions in terms of conservation of energy

A

chemical system releases heat energy to the surrounding
any energy loss by the chemical system is balanced by the energy gain by surroundings
enthalpy change is negative
the temp of the surroundings increases as they gain enrgy

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11
Q

what happens in endothermic reaction in terms of conservation of energy

A

chemical system takes in heat from surroundings
any energy gain by chemical system is balanced by the same energy loss by the surroundings
Enthalpy change is positive
the temperature of the surroundings decrease as they lose energy

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12
Q

What is activation energy

A

minimum energy required for a reaction to take place

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13
Q

what happens to reactions with small activation energy

A

reactions take place very rapidly because energy needed to break bonds are readily availablefrom the surroundings

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14
Q

what happens to reactions with large amount of activation energy

A

such a large energy barrier that reaction may take place extremly slowlyor even not at all

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15
Q

what are the standard conditions

A

standard pressure- 100 Kpa
standard temperature - 298K
standard concentration - 1 mol dm^-3
standard state -100 kpa and 298K

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16
Q

what is the standard enthalpy change of reaction

A

is the enthalpy change that accompanies a reaction in the molar quantities shown in a chemical equation under standard conditions with all reactant and products in their standard state

17
Q

what is the standard enthalpy change of formation

A

is the enthalpy change that takes place when one ,mole of a compound is formed from its elements under standard conditions with all reactant and products in their standard state

18
Q

what is the standard enthalpy change of combustion

A

is the enthalpy change that takes place when one mole of a substance reacts completely with oxygen under standard conditions with all reactant and product in their standard states

19
Q

what is the enthalpy change of neutralisation

A

is the energy change that accompanies a reaction of an acid by a base to form one mole of H2O(l) under standard conditions with all reactants and products in their standard conditions

20
Q

what is the formula for calculating energy change

A

Q=MC(change in temp)
Q=heat energy (J)
M= mass (g)
c= specific heat capacity
temp = the value of temp is exactly the same in degrees and kelvin

21
Q

why are reactions less exothermic than we expect it

A

heat loss
incomplete combustion
non standard conditions

22
Q

what could minimise error from heat loss and incomplete combustion

A

use of draught screens and oxygen gas

23
Q

how can we determine the enthalpy change of reaction

A

using plastic cups made of polystyrene foam . These are cheap lightweight and offer some insulation against heat loss to surroundings

24
Q

what happens when carrying out a reaction between aqeous solutions

A

the solution itself is the immediate surroundings. The chemical particles within the solution may react when collide and any energy transfer is between the chemical particles and water molecules in the solution a thermometer in the solution will record any temperature change to be calculated using mcat

25
Q

what is average bond enthalpy

A

is the energy required to break one mole of a specified type of bond in a gaseous molecule

26
Q

what is always required is break bonds

A

energy

27
Q

what type of reaction is bond enthalpy

A

endothermic so always have positve value

28
Q

what are limitations of bond enthalpies

A

vary depending on the chemical environment of the bond

29
Q

what is bond breaking

A

endothermic

30
Q

what is bond making

A

exothermic

31
Q

State Hess’ Law

A

if a reaction can take place by two routes and the starting and finishing conditions are the same the total enthalpy change is the same for each route

32
Q

What is the calculation for the enthalpy change in formation

A

Product - reactant

33
Q

What is the calculation for enthalpy change in combustion

A

Reactant-product

Inorganic Chem AS level (6 decks)

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