Energetics, equilibrium. reversible reactions

Question 1

define exothermic

Answer 1

A reaction that releases energy into it’s surroundings,usuaslly in the form of heat and shown by a rise in temperature.

Question 2

In terms of bonds, what does an exothermic reaction involve?

Answer 2

New bonds are being formed to create the products of the reaction. Energy is released when the bonds are formed.

Question 3

define endothermic

Answer 3

A reaction which involves bonds being broken, absorbs energy from it’s surroundings, usually in the form of heat and shown by a fall in temperature

Question 4

In terms of bonds, what does an endothermic reaction involve?

Answer 4

Bonds of the reactants are being broken. Energy is absorbed in order to do this.

Question 5

what is enthalpy change?

Answer 5

the overall change in energy in a reaction.

Question 6

the enthalpy equation.

Answer 6

enthalpy change = total energy absorbed in breaking bonds - total energy released in making bonds

Question 7

what is the unit for energy in enthalpy measurements?

Answer 7

jk/mol

Question 8

what value of jk/mol would an endothermic reaction have?

Answer 8

+ve

Question 9

what value of jk/mol would an exothermic reaction have?

Answer 9

-ve

Question 10

what is activation energy?

Answer 10

the minimum amount of energy required to start a reaction

Question 11

what effect would a catalyst have on the speed of a reaction? the activation energy?

Answer 11

a catalyst would INCREASE THE SPEED of a reaction by providing another way for the paritcles to react with a LOWER activation energy.

Question 12

what effect woulf a catalyst have on the overall energy change of a reaction?

Answer 12

None. It stays the same.

Question 13

where is the enthalpy shown on an energy level diagram?

Answer 13

between the reactants and the products

Question 14

what goes along the bottom of an energy level diagram? Up the side?

Answer 14

progress of reaction along the bottom, energy up the side.

Question 15

describe an energy level diagram of an endothermic reaction.

Answer 15

the reactants are lower on the energy scale than the products because energy has been absorbed over the course of the reaction

Question 16

describe an energy level diagram of an exothermic reaction.

Answer 16

the reactants are higher than the products on the energy scale because energy has been released over the course of the reaction.

Question 17

what is Lechatilier’s principal?

Answer 17

any change made to a reaction which is in equilibrium, will result in the equilibrium position moving to minimise the change made

Question 18

Define dynamic equilibrium

Answer 18

The forwards and backwards reactions are taking same place but at exactly the same rate so the relative quantities of products and reactants remains the same

Question 19

What does the postion of the equilibrium depend on?

Answer 19

Temperature and pressure

Question 20

What happens if you alter the pressure or temperature?

Answer 20

You move the position of the equilibrium to give more or less products or reactants

Question 21

What happens if you raise the temperature

Answer 21

the endothermic reaction will increase to use up the extra heat

Question 22

what happens if you lower the temperature

Answer 22

The equilibrium will shift to favour the exothermic reaction the minimise the decrease in temperature

Question 23

If the reaction that formed ammonia was exothermic what would happen to the yield of ammonia if you increased the temperature?

Answer 23

It would decrease because it would favour the endothermic reaction to use up the extra heat. (the endothermic reaction does not produce ammonia)

Question 24

give an exmaple of a reversible reaction

Answer 24

the thermal decomposition of ammonium chloride

Question 25

give equation for the thermal decomposition of ammonium chloride

Answer 25

NH4CL(s) -> NH3(g) + HCL(g)

Question 26

what is another example of a reversible reaction?

Answer 26

The dehyration of coppper sulfate

Question 27

define a reversible reaction

Answer 27

A reversible reaction is one where the products of a reaction can then themselves react to produce the original reactants

Question 28

What happens if you alter the pressure in a reversible reaction (raise or lower)

Answer 28

most gaseous reactions have more molecules/ moles of gas on one side than the other

• raising the pressure will encourage the reaction that produces fewer molecules.
• lowering the pressure will encourage the reaction which produces more molecules