Energy Changes (5076/5078 syllabus)

Ener gy Changes 1 Energy Changes Endothermic Reaction 1. Involves breaking of bonds 2. Decrease in temp Reaction of Ammonium Chloride and Water (endothermic) https://www.youtube.com/watch?v=a-nfY5acelc Visualisation of Endothermic Reaction (energy is absorbed from the surroundings): Photosynthesis: P h o t o s y n t h e s i s i s e n d o t h e r m i c b e c a u s e , l i g h t e n e r g y i s t a k e n i n b y t h e l e a v e s f o r i t t o o c c u r

Ener gy Changes 2 Thermal decomposition: a chemical reaction where heat is THE reactant. (implies that it requires thermal energy to break the chemical bonds of the molecules) Exothermic Reaction 1. Rise in Temp 2. Involve bond formation Visualisation of an exothermic reaction (energy is released into the surrounding) oxidation= any form of reaction with oxygen counts as exothermic reaction rusting freezing: heat is being ‘removed’ and released into the surroundings ENDOTHERMIC VS EXOTHERMIC Type of reaction Endothermic Exothermic Temperature Change Decrease (cooler temperature)Increases (hotter temperature)

Ener gy Changes 3 Energy Change Net Absorption of energy FROM the surrounding Net Release of energy INTO the surrounding Changes in bonding breaks bond forms bonds Change in enthalpy (ΔH) +ve -ve ΔH (Δ=Delta H=enthalpy) freezing and condensation= more orderly particles → heat loss (exothermic) melting, boiling and sublimation=more disorderly → energy absorbed (endothermic)