Energetics Flashcards
What is an exothermic reaction?
A reaction that gives out heat energy to the surroundings
What are examples of an exothermic reaction?
Combustion
Neutralisation
What is an endothermic reaction?
A reaction that takes in heat energy from the surroundings
What are examples of an endothermic reaction?
Photosynthesis
Thermal decomposition
Draw the reaction profile of an exothermic reaction
Well done
Draw the reaction profile of an endothermic reaction
Well done
What is the enthalpy change of a system?
The heat energy change at constant pressure
What are the standard conditions for enthalpy change?
100kPa and stated temperature (usually 298K)
What is the standard enthalpy change of formation?
Enthalpy change when 1 mole of a substance is formed from its constituent elements with all reactants and products in standard states under standard conditions
What is the standard enthalpy change of combustion?
Enthalpy change when 1 mole of a substance is completely burned in oxygen with all reactants and products in standard states under standard conditions
What is the standard enthalpy of neutralisation?
Enthalpy change when 1 mole of water is formed in a reaction between an acid and an alkali under standard conditions
How much energy does it take to raise the temperature of 1g of water by 1°C?
4.18 J
What equation can be used to find the amount of heat energy given out / absorbed in a reaction?
q = m x c x change in temp
q (heat energy given out - J)
m (mass - g)
change in temp (K)
c (specific heat capacity - J g-1K-1)
What equation can we use to find the enthalpy change of a reaction?
Enthalpy change = q ÷ number of moles reacting
What is Hess’s Law?
The enthalpy change for a reaction is independent of the route taken
How do you calculate overall enthalpy change for enthalpy of formation?
Sum of products - sum of reactants
What is the enthalpy of formation of an element?
0
How do you calculate the overall enthalpy change for enthalpy of combustion?
Sum of reactants - sum of products
How do you calculate the overall enthalpy change when working with bond enthalpies?
Sum of bonds broken - sum of bonds made
(reactants - products)
What is mean bond enthalpy?
The energy required to break a covalent bond averaged over a range of different compounds
