chemical energetics

Chemical Energetics

​OBJECTIVES

Open Ended

in your mind, what are we going to study in this chapter?

​in this chapter, we will study

1. graphing related to energy transfer

2. stoichiometry related computation

3. more to physical chemistry

4. renewable energy

​EXOTHERMIC REACTION

​LETS TRY THE SIMPLE EXPERIMENT

on your table, you are provided with beaker distilled water and one boat.

transfer around 50 cm3 of distilled water to beaker, then add pellets of NaOH

observe the temperature change

​picture from Cambridge IGCSE and O Level Complete Chemistry Fourth ed , Oxford University Press

Draw

sketch your graph below (temperature against time)

Multiple Select

describe the EXOTHERMIC reaction

tick the correct statement

• temperature increases

• temperature decreases

• container feels warmer

• the reaction is written as follows

  reactant → product + thermal energy

• the reaction is written as follows

  reactant + thermal energy → product

Multiple Select

list down the example of exothermic reaction

• combustion of fuel

• photosynthesis

• respiration

• neutralisation

• thermal decomposition

​energy level of the product is lower than the reactant since energy is being RELEASED.

the transfer of energy is from SYSTEM to SURROUNDING

enthalpy change values

(-) negative sign

​ENDOTHERMIC REACTION

​LETS TRY THE SIMPLE EXPERIMENT

on your table, you are provided with beaker, distilled water and one boat.

transfer around 50 cm3 of distilled water to beaker, then add solid of NH4Cl

observe the temperature change

​picture from Cambridge IGCSE and O Level Complete Chemistry Fourth ed , Oxford University Press

Draw

sketch the diagram of temperature against time for dissolving of NH4Cl

Multiple Select

describe the ENDOTHERMIC reaction

tick the correct statement

• temperature increases

• temperature decreases

• container feels colder

• the reaction is written as follows

  reactant → product + thermal energy

• the reaction is written as follows

  reactant + thermal energy → product

Multiple Select

list down the example of endothermic reaction

• corrosion of iron

• photosynthesis

• action of light towards the conventional photographic film

• neutralisation

• thermal decomposition

​energy level of the product is higher than the reactant since energy is being ABSORBED.

the transfer of energy is from SURROUNDING to SYSTEM

enthalpy change values

(+) negative sign

ENERGY LEVEL DIAGRAM,

IN CONNECTION WITH ACTIVATION ENERGY

​energy level diagram

​activation energy is the minimum energy that colliding particles must have , in order to react.

​picture from Cambridge IGCSE and O Level Complete Chemistry Fourth ed , Oxford University Press

​how sufficient energy is supplied?

• for exothermic reaction, if the energy from the surrounding is sufficient. mixing the reactant without heating will do.

• some exothermic reaction, heating from bunsen burner is needed to start the reaction.

• single spark from motor allows some reactions occurred.

• for endothermic reaction, which requires very high activation energy, heating must be kept until the reaction is complete.

​bond energy and lead to the calculation of enthalpy change

​

​picture from Cambridge IGCSE and O Level Complete Chemistry Fourth ed , Oxford University Press

​

​picture from Cambridge IGCSE and O Level Complete Chemistry Fourth ed , Oxford University Press

​

​picture from Cambridge IGCSE and O Level Complete Chemistry Fourth ed , Oxford University Press

Multiple Choice

Which letter corresponds to the energy of the products?

• A

• B

• C

• D

Multiple Choice

Which statements about exothermic and endothermic reactions are correct?

1      During an exothermic reaction, heat is given out.

2      The temperature of an endothermic reaction goes up because heat is taken in.

3      Burning methane in the air is an exothermic reaction.

• 1, 2, and 3

• 1 and 2 only

• 1 and 3 only

• 2 and 3 only

Multiple Choice

Which row describes an endothermic reaction?

• A

• B

• C

• D

Open Ended

Hydrogen reacts with oxygen in a fuel cell.

 

2H₂ + O₂ → 2H₂O

 

The reaction is exothermic. 

286 kJ of energy is released for every mole of water formed.

 

Which volume of hydrogen gas, measured at room temperature and pressure, would react with oxygen with the release of 7000 J of energy?

Open Ended

Chlorine reacts with ethane to produce chloroethane and hydrogen chloride.