Endothermic And Exothermic Reations

Question 1

Thermochemistry

Answer 1

Study of heat changes during a chemical reaction
• when reaction takes place, bonds break and new ones are formed
• energy put in to break bonds and energy gave out when formed
• exothermic = energy given out
• endothermic = energy taken in
• reaction is endothermic one way and exothermic in the reverse

Question 2

Endothermic reactions

Answer 2

• reaction that gives out heat
• neutralising an acid with alkali
EXAMPLE
ADDITION OF WATER TO COPPER SULFATE GIVES OUT HEAT

Question 3

Endothermic reactions

Answer 3

• takes in heat from its surroundings
EXAMPLE
HEAT ENERGY ADDED TO BREAK BONDS BETWEEN WATER AND COPPER SULFATE
• ENERGY SUPPLIED SO ENDOTHERMIC

Question 4

Quantity of reactants

Answer 4

Amount of energy produced depends on the quantity of reactants

EXAMPLE
one mole of methane reacts with two moles of oxygen
CH4 + 2O2 —> CO2 + 2H2O
890kJ given out making the reaction exothermic

Question 5

Useful enthalpy changes

Answer 5

When fuels burn there is a large heat output meaning very exothermic
EXAMPLE
C + O2 —> CO2 393.5kJ

ENDOTHERMIC
NH4NO3 (s) + (aq) —> NH4NO3 (aq)
Absorbs 26kJ mol-1