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Chemistry, Module 3 OCR > Enthalpy Changes > Flashcards

Flashcards in Enthalpy Changes Deck (16)
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1
Q

Endothermic reactions

A

Enthalpy of products> enthalpy of reactants

System absorbs heat from surroundings: More energy taken in making bonds, than released breaking bonds.

Give +/ve values

2
Q

Exothermic

A

Enthalpy of products

3
Q

System

A

Reactant and products

4
Q

Surroundings

A

Environment outside chemical system

5
Q

Standard enthalpy change of reaction (3)

A

Standard conditions

Reactants and products in standard state

Molar quantities as expresses in chemical equation

6
Q

Standard enthalpy change of combustion (4)

A

Complete combustion

1 mole of substance reacts completely with O2

Standard conditions

Reactants and products in standard states

7
Q

Standard enthalpy change of formation (3)

A

1 mol of product is formed

Standard conditions

Reactants elements in natural states

8
Q

Standard enthalpy change of neutralisation (3)

A

1 mol of water formed in acid-base neutralisation

Standard conditions

Usually -57 KJmol-

9
Q

Enthalpy

A

Heat contender stored in chemical system

10
Q

Activation energy

A

Minimum energy required to start a reaction by breaking of bonds

11
Q

Atom economy

A

(Sum of molar masses of desired products) x (sum of molar masses of all products)

12
Q

Average bond enthalpy

A

The average enthalpy change that takes place when breaking;

  • by homolytic fission
  • 1 mol of a given type of bond in the molecules of a gaseous species.
14
Q

What is the formula for finding how much heat has been transferred in a reaction?

A

Q= Mc🔺T

Mass of surroundings x specific heat capacity x difference in temperature

15
Q

Formula for enthalpy change

A

-Q/ n

Heat transferred/ number of moles

16
Q

What are the standard conditions

A
  • 298K

- 101 kPa

17
Q

What are the standard conditions

A
  • 298K