Unit 3 - Physical Chemistry Flashcards
(17 cards)
Define what is meant by ‘enthalpy change.’
The heat energy transferred in a reaction at constant pressure
Define what is meant by ‘standard states.’
Physical states a molecule is in under standard conditions
State what the standard conditions are.
- 100kPa
- 298K
What is meant by the ‘⦵’ symbol?
Standard conditions
Define what is meant by ‘standard enthalpy change of reaction.’
- The enthalpy change when a reaction occurs in the molar quantities shown in the chemical equation
- With all reactants and products in their standard states
- Under standard conditions
Define what is meant by ‘standard enthalpy change of neutralisation.’
- The enthalpy change when solutions of an acid and alkali react together
- To form 1 mole of water
- Under standard conditions
Define what is meant by ‘standard enthalpy change of combustion.’
- The enthalpy change when 1 mole of a substance
- Is completely burned in oxygen
- Under standard conditions
Define what is meant by ‘standard enthalpy change of formation.’
- The enthalpy change when 1 mole of a compound is formed
- From it’s elements inn their standard states
- Under standard conditions
Define what is meant by the term ‘activation energy.’
The minimum amount of energy needed for a reaction to start
Define what is meant by an ‘exothermic reaction.’
- The energy released by bond forming is greater than the energy required for bond breaking
- Negative enthalpy change
Define what is meant by an ‘endothermic reaction.’
- The energy required for bond breaking is greater than the energy released from bond forming
- Positive enthalpy change
Define the term ‘average bond enthalpy.’
- Average enthalpy change
- When one mole of gaseous covalent bonds are broken
Define what is meant by ‘a catalyst.’
- Catalysts increase the rate of reaction
- By providing an alternate reaction pathway with a lower activation energy
- The catalyst is chemically unchanged at the end of the reaction
Define what is meant by the ‘rate of reaction.’
The change in the number of reactants or products per unit of time
Explain what is meant by collision theory in terms of how molecules react.
- Particles in liquids and gases are moving and collide with each other - they do not always react
- They need to collide in the correct orientation
- They need to collide with at least a certain minimum amount of kinetic energy - the activation energy
Describe what is meant by a ‘homogenous catalyst.’
The catalyst is in the same physical state as the reactants
Describe what is meant by a ‘heterogenous catalyst.’
The catalyst is in a different physical state to the reactants
