Unit 3- Chemistry in Society

Question 1

What is raw material and examples?

Answer 1

Natural resources-
e.g. fossil fuels, metallic ores, air, water and salt.

Question 2

What is feedstock and examples?

Answer 2

Reactive components extracted from raw material by a chemical process -
e.g. ethene, benzene

Question 3

What is consumer product and examples?

Answer 3

Product manufactured for use in society.

Question 4

What is the formula for Molar Volume?

Answer 4

n=V/Mv
Mv=V/n
V=n.Mv

Question 5

What is the formula for Percentage Yield?

Answer 5

The quality of product formed is called a theoretical yield.
%yield = actual yield/theoretical yield x 100

Actual - in question
Theoretical - moles of reactant x GFM of product

Question 6

What is the formula for Atom Economy?

Answer 6

Atom economy measures the proportion of the total mass of reactants that is successfully converted into the desired product.
%atom economy = mass of desired product(s)/total mass of reactants x 100

If only one product, the atom economy is 100%.

Question 7

How to investigate the effect of changing concentration on rate of reaction?

Answer 7

• make a series of dilutions of acid.
• react the same volume of acid with the same volume of chalk (CaCO3).
• Record results.
• Calculate an average rate for each.

Question 8

What happens if there is a decrease in concentration?

Answer 8

There will be less particles in the same volume, which means there will be less collisions. Therefore the rate of reaction slows down.

Question 9

What is the relative rate?

Answer 9

1/t
The relative rate can be used to investigate the effect of factors such as temperature and concentration on the rate of reaction.

Question 10

In collision theory, what do the reactant particles need to react?

Answer 10

• with energy greater than or equal to the activation energy.
• with the correct collision geometry or angle.

Question 11

What is activation energy?

Answer 11

the minimum kinetic energy with which particles have to collide in order to react.

Question 12

What is the activated complex?

Answer 12

an unstable arrangement of atoms, intermediate between reactants and products, formed at the maximum of the potential energy barrier, during a reaction.

Question 13

What is temperature a measure of?

Answer 13

the average kinetic energy of all the particles in a substance.

Question 14

How does rate of reaction increase with temperature increase?

Answer 14

The average kinetic energy of the particles increases and a greater proportion of reactant particles collide with energy greater than or equal to the activation energy.

Question 15

What is a catalyst used for?

Answer 15

• a catalyst is a substance that speeds up a chemical reaction without being chemically changed.
• a biological catalyst is called an enzyme.
• a catalyst can provide a surface for reactions to take place on.

Question 16

What does a catalyst provide?

Answer 16

an alternative reaction pathway with a lower activation energy.

Question 17

Examples of catalysts used in industry?

Answer 17

• Iron - used to make ammonia by the Haber Process.
• Platinum - used in manufacture of nitric acid (Ostwald Process)
• Nickel - used to make margarine by hardening vegetable oil.

Question 18

What is the enthalpy change?

Answer 18

the energy difference between the products and the reactants and is the overall enthalpy change for a reaction.

Question 19

Exothermic reaction pathways?

Answer 19

assigned a negative △H value.
reactants are higher than products.
Ea is from the peak of the curve to the reactants line.
△H is from reactants line to products line.

Question 20

Endothermic reaction pathways?

Answer 20

assigned a positive △H value.
reactants are lower than products.
Ea is from peak of the curve to the reactants line.
△H is from the reactants line to the products line.

Question 21

What is the general rule for bond breaking/making?

Answer 21

bond BREAKING is always endothermic (+△H)
bond MAKING is always exothermic (-△H)

Question 22

What is exothermic?

Answer 22

RELEASE heat to the surroundings.

Question 23

What is endothermic?

Answer 23

ABSORB heat from the surrundings.

Question 24

Why is it important to know if a reaction in industry is exothermic?

Answer 24

quantity of heat released, to knw how much heat has to be removed to prevent it from becoming too hot.

Question 25

Why is it important to know if a reaction in industry is endothermic?

Answer 25

cost of fuel required to maintain temperature of the reaction.

Question 26

What is the enthalpy of combustion?

Answer 26

(△Hc) The enthalpy of combustion of a substance is the energy released when one mole of a substance is burned completely in oxygen.

Question 27

What is the formula to measure enthalpy of combustion?

Answer 27

Eh=cm△T △H=Eh/n

Question 28

What does Hess's Law state?

Answer 28

The enthalpy change for a chemical reaction is independant of route.

Question 29

What is the bond enthalpy?

Answer 29

the energy required to break one mole of a particular bond between a pair of atoms in the gaseous state.

Question 30

What is the MEAN bond enthalpy?

Answer 30

an average value.

Question 31

When is a reaction at equilibrium?

Answer 31

when the rate of the forward and reverse reaction are equal and the concentration of reactants and products remain constant.

Question 32

Where can equilibrium be established?

Answer 32

In a closed system ONLY.

Question 33

How to tell the position of equilibrium?

Answer 33

If the concentration of reactants is greater than the products at equilibrium, we say the position of the equilibrium lies to the left. If the concentration of products is greater than the reactants at equilibrium, we say the position of the equilibrium lies to the right.

Question 34

What does Le Chantelier's principle state?

Answer 34

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

Question 35

What is the effect of changing concentration? Co(H2O)6pink + 4Cl <--> CoCl4blue + 6H2O

Answer 35

Increasing the concentration of Cl, increases the rate of the forward reaction, compared to the reverse, increasing the concentration of products. The equilibrium has shifted to the right so the solution becomes more blue in colour. Increasing the concentration of CoCl4, increases the rate of the reverse reaction, compared to the forward, increasing the concentration of reactants. The equilibrium has shifted to the left so the solution becomes more pink in colour.

Question 36

What is the effect of changing pressure? 2NO2(g)brown <--> N2O4(g)pale yellow

Answer 36

(Equilibria which involve gases can be affected by changes in pressure) Increasing pressure will increase the rates of the forward and the reverse reactions. The rate of the forward reaction increases more as increasing pressure favours the reaction that reduces the number of moles of gas at equilibrium. Increasing pressure will cause the colour of the equilibrium mixture to become paler. Decreasing pressure will decrease the rates of the forward and the reverse reactions. The rate of the forward reaction decreases more as decreasing pressure favours the reaction that increases the number of moles of gas at equilibrium. Decreasing pressure will cause the colour of the equilibrium mixture to become darker.

Question 37

What is the effect of changing temperature? EG1: N2O4(g)pale yellow <--> 2NO2(g)brown △H= +ve

Answer 37

If the temperature is increased the rates of the forward and the reverse reactions increase. The rate of the forward reaction increases more as increasing temperature favours the endothermic reaction. This would shift the equilibrium right and the colour of the reaction mixture will become darker.

Question 38

What is the effect of changing temperature? EG2: 2NO2(g)brown <--> N2O4(g)pale yellow △H= -ve

Answer 38

Increasing the temperature, the rate of the forward and reverse reactions increase. The rate of the reverse reaction increases more as increasing temperature favours the exothermic reaction. The position of equilibrium will lie to the left and the colour will appear darker.

Question 39

What can be used to remove ions from an equation?

Answer 39

AgNO3

Question 40

What is the effect of a catalyst?

Answer 40

NO EFFECT!