Chemistry - 4CH1 PearsonEdexcel

Energetics

Gbogbo ọrọ náà

Why does a hand warmer get hot? Why does a cold pack feel cold even though no ice is inside? The answers lie in energetics: the study of heat changes during chemical reactions. Some reactions release energy to the surroundings; others absorb it.

In this lesson you will learn to classify reactions as exothermic or endothermic, measure heat changes using calorimetry, draw energy level diagrams, and use bond energies to predict whether a reaction gives out or takes in heat. These calculations and diagrams are tested heavily across both Edexcel papers.

Ebumnobi

know that chemical reactions in which heat energy is given out are described as exothermic, and those in which heat energy is taken in are described as endothermic
describe simple calorimetry experiments for reactions such as combustion, displacement, dissolving and neutralisation
calculate the heat energy change from a measured temperature change using the expression Q = mcΔT
calculate the molar enthalpy change (ΔH) from the heat energy change, Q
draw and explain energy level diagrams to represent exothermic and endothermic reactions
know that bond-breaking is an endothermic process and that bond-making is an exothermic process
use bond energies to calculate the enthalpy change during a chemical reaction
practical: investigate temperature changes accompanying some of the following types of change: - salts dissolving in water - neutralisation reactions - displacement reactions - combustion reactions.

Akọmọ Ojú-ẹkọ

Strike a match and you feel warmth. Dissolve ammonium nitrate in water and the beaker goes cold. Every chemical reaction involves an energy change, and understanding which direction the energy flows is central to chemistry. Energetics connects the microscopic world of bond breaking and bond making to the macroscopic temperature changes you can feel and measure.

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Ayẹwo Ẹkọ

Ekele diri gi maka imecha ihe karịrị na Energetics. Ugbu a na ị na-enyochakwa isi echiche na echiche ndị dị mkpa, ọ bụ oge iji nwalee ihe ị ma. Ngwa a na-enye ụdị ajụjụ ọmụmụ dị iche iche emebere iji kwado nghọta gị wee nyere gị aka ịmata otú ị ghọtara ihe ndị a kụziri.

Ị ga-ahụ ngwakọta nke ụdị ajụjụ dị iche iche, gụnyere ajụjụ chọrọ ịhọrọ otu n’ime ọtụtụ azịza, ajụjụ chọrọ mkpirisi azịza, na ajụjụ ede ede. A na-arụpụta ajụjụ ọ bụla nke ọma iji nwalee akụkụ dị iche iche nke ihe ọmụma gị na nkà nke ịtụgharị uche.

Jiri akụkụ a nke nyocha ka ohere iji kụziere ihe ị matara banyere isiokwu ahụ ma chọpụta ebe ọ bụla ị nwere ike ịchọ ọmụmụ ihe ọzọ. Ekwela ka nsogbu ọ bụla ị na-eche ihu mee ka ị daa mba; kama, lee ha anya dị ka ohere maka ịzụlite onwe gị na imeziwanye.

Which of the following is an endothermic process? A) Combustion of methane B) Neutralisation of acid and alkali C) Thermal decomposition of calcium carbonate D) Displacement of copper by iron Answer: C
In an exothermic reaction, the energy level diagram shows: A) Products higher than reactants B) Products lower than reactants C) Products and reactants at the same level D) No activation energy Answer: B
Bond breaking is always: A) Exothermic B) Endothermic C) Neutral D) Impossible to predict Answer: B
The specific heat capacity of water is: A) 4.18 J g-1 K-1 B) 4.18 kJ g-1 K-1 C) 41.8 J g-1 K-1 D) 0.418 J g-1 K-1 Answer: A
What does the activation energy represent on an energy level diagram? A) The total energy released B) The energy of the products C) The minimum energy needed to start the reaction D) The energy stored in the bonds Answer: C