6 Chemical reactions

Question 1

physical change

Answer 1

dosen’t make new chemical and are usually easy to reverse

Question 2

chemical change

Answer 2

chemical bonds between atoms are broken and made, so the atoms get rearranged into new substances

Question 3

catalyst

Answer 3

increases the rate of a reaction and is unchanged at the end of a reaction

(decreasesthe activation energy by providing an alternate pathway with lower activation energy)

Question 4

collision theory

Answer 4

chemical reactions occur when the reactant particles collide with sufficient energy to react and proper orientations

Question 5

effect on temperature on rate of reaction

Answer 5

when the temperature is increased, the particles speed increase due to higher kinetic energy. Resulting in the particles colliding more frequently. As well as having more particles that have the necessary activation energy to break bonds.

Question 6

effect of concentration on rate of reaction

Answer 6

Doubling the concentration will also double the number of collisions. Increasing the concentration of either reactant increases the number of collisions and therefore increases the number of sucessful collisions and the reaction rate.

Question 7

effect of surface area on rate of reaction

Answer 7

Increasing the surface area increases the frequency of collisions and reaction rate. As reactants are more exposed to the other reactants.

Question 8

effect of catalyst on activation energy

Answer 8

a catalyst decreases the activation energy of a reaction

Question 9

An investigation to measure rate of reaction using different surface areas

Answer 9

Method:
- dilute HCl into a conical flask
- use a delivery tube to connect this flask to a measuring cylinder upside down in a bucket of water (downwards displacement)
- add CaCO3 chips into the conical flask and quickly put the bung back into the flask
- measure the volume of gas produced in a fixed time using the measuring cylinder
- repeat with different sizes of CaCO3 chips (lumps, crushed and powdered)

Question 10

redox reactions

Answer 10

involving simultaneous
oxidation and reduction

Question 11

oxidation

Answer 11

loss of electrons
gain of oxygen
increase in oxidation number

Question 12

reduction

Answer 12

gain of electrons
loss of oxygen
decrease in oxidation number

Question 13

when is a reversible reaction in equilibrium

Answer 13

a) the rate of the forward reaction is equal to the rate of the backward reaction
b) the concentration of reactants and products are constant

Question 14

When temperature increases what happens to the position of equilibrium?

Answer 14

Shifts the equilibrium in the direction of the endothermic reaction

Question 15

When pressure increases what happens to the position of equilibrium?

Answer 15

Shifts the equilibrium towards the side with the fewer moles of gas

Question 16

When the concentration of a substance changes what happens to the position of the equilibrium?

Answer 16

The equilibrium will shift to minimise the effect of the change.
- If the concentration of a reactant (on the left) is increased, the equilibrium position moves in the direction away from this reactant, and so more of the products are produced (on the right).

Question 17

When a catalyst is added what happens to the position of the equilibrium?

Answer 17

There is no effect on the position of equilibrium. However it does allow equilibrium to be reached more quickly, or estabilished at a lower temperature, which makes reactions more profitable.

Question 18

Haber Process symbol equation

Answer 18

N2(g) + 3H2(g) <–> 2NH3(g)

Question 19

source of hydrogen in the haber process

Answer 19

Methane

Question 20

source of nitrogen in the haber process

Answer 20

Air

Question 21

Typical conditions of the haber process

Answer 21

450C, 20000 kPa/200 atm, and an iron catalyst

Question 22

Source of sulfur dioxide in the contact process

Answer 22

burning sulfur or roasting sulfide ore

Question 23

Source of oxygen in the contact process

Answer 23

air

Question 24

typical conditions for the conversion of sulfur dioxide to sulfur trioxide in the contact process

Answer 24

450C, 200kPa/2 atm and a vanadium(V) oxide catalyst

Question 25

Explain, in terms of rate of reaction and position of equilibrium, why the typical conditions stated are used in the Haber process and in the Contact
process,

Answer 25

Temperature
low enough to achieve an acceptable yield
high enough to do this in an acceptable time
Pressure
low enough to keep costs down
high enough to achieve an acceptable yield

Question 26

Acidified Potassium manganate (VII) purpose

Answer 26

Acidified potassium manganate (VII) is an oxidising agent.
- from purple to colourless

Question 27

Aqueous potassium iodide purpose

Answer 27

Aqueous potassium iodide is a reducing agent
- from colourless to yellow-brown

Question 28

observations of NO2

Answer 28

brown gas and pungent smell