Chemical industry

Question 1

What is the rate of reaction?

Answer 1

The rate of reactant-to-product conversion, calculated as the gradient of a concentration-time graph.

Question 2

What is the general form of the rate equation?

Answer 2

rate = k[A]^a[B]^b, where k is the rate constant, [X] is the concentration, and a, b are the orders of reactants.

Question 3

What happens to the rate constant (k) as temperature increases?

Answer 3

The rate constant (k) increases with temperature.

Question 4

What is the order of a reaction?

Answer 4

An integer determined experimentally that shows how the rate depends on the concentration of a specific reactant.

Question 5

What is overall order in a reaction?

Answer 5

The sum of all individual orders in the reaction.

Question 6

How can you determine the order of a reactant?

Answer 6

Measure how the rate changes as the concentration of that reactant doubles, ensuring other reactants are in excess.

Question 7

What is a zero-order reaction?

Answer 7

A reaction where the rate is independent of the concentration of the reactant.

Question 8

What is a first-order reaction?

Answer 8

A reaction where the rate is directly proportional to the concentration of the reactant.

Question 9

What is a second-order reaction?

Answer 9

A reaction where the rate is proportional to the square of the concentration of the reactant.

Question 10

What is reaction half-life?

Answer 10

The time it takes for half of a reactant to be used up.

Question 11

What does a constant half-life indicate?

Answer 11

A first-order reaction.

Question 12

What is the equation to calculate the rate constant (k) for first-order reactions?

Answer 12

k = ln(2) / t1/2 (units: s⁻¹).

Question 13

What is the initial rate of reaction?

Answer 13

The rate at the start of the reaction, calculated as amount of reactant used or product formed divided by time.

Question 14

What is a clock reaction?

Answer 14

A reaction with a clear endpoint (e.g., a color change), useful for measuring the initial rate of reaction.

Question 15

Describe the iodine clock reaction.

Answer 15

H₂O₂ + 2I⁻ + 2H⁺ → 2H₂O + I₂, where sodium thiosulfate removes I₂ until it is used up, producing a color change with starch.

Question 16

What does a zero-order concentration-time graph look like?

Answer 16

A straight line with a negative gradient.

Question 17

What does a first-order concentration-time graph look like?

Answer 17

An exponential decay curve.

Question 18

What does a second-order concentration-time graph look like?

Answer 18

A steeper exponential decay curve than first order.

Question 19

What does a zero-order rate-concentration graph look like?

Answer 19

A horizontal line (rate is constant regardless of concentration).

Question 20

What does a first-order rate-concentration graph look like?

Answer 20

A straight line with a positive gradient.

Question 21

What does a second-order rate-concentration graph look like?

Answer 21

A quadratic curve.

Question 22

What is the Arrhenius equation?

Answer 22

k = Ae^(-Ea/RT), where k is the rate constant, Ea is activation enthalpy, T is temperature (K), R is the gas constant, and A is the pre-exponential factor.

Question 23

How can the Arrhenius equation be rearranged for plotting?

Answer 23

ln(k) = -Ea/RT + ln(A), allowing a plot of ln(k) against 1/T with gradient -Ea/R.

Question 24

What is the rate-determining step?

Answer 24

The slowest step in a multi-step reaction, determining the overall reaction rate.

Question 25

What does it mean if a reactant is not in the rate equation?

Answer 25

The reactant is not involved in the rate-determining step.

Question 26

How does changing pressure affect the equilibrium constant (Kc)?

Answer 26

Pressure does not affect Kc, but it shifts the equilibrium position toward fewer moles of gas.

Question 27

How does changing concentration affect Kc?

Answer 27

Concentration changes shift equilibrium but do not affect the value of Kc.

Question 28

How does temperature affect Kc?

Answer 28

Temperature changes affect both the equilibrium position and the value of Kc.

Question 29

What is the effect of adding a catalyst on equilibrium?

Answer 29

It does not affect Kc or the equilibrium position but reduces the time taken to reach equilibrium.

Question 30

How can Kc be determined experimentally?

Answer 30

Using colorimetry for colored substances or pH probes for acidic/alkaline equilibria.

Question 31

What is the structure of nitrogen (N2)?

Answer 31

A diatomic molecule with a triple bond, giving it a very high bond enthalpy.

Question 32

What is the structure of ammonia?

Answer 32

NH3 with a lone pair of electrons.

Question 33

What is the formula of the ammonium ion?

Answer 33

NH4⁺.

Question 34

What is nitrogen monoxide?

Answer 34

NO, a colorless gas also called nitrogen(II) oxide.

Question 35

What is dinitrogen monoxide?

Answer 35

N2O, a colorless gas with a sweet smell, also called nitrogen(I) oxide or laughing gas.

Question 36

What is nitrogen dioxide?

Answer 36

NO2, a brown gas with a sharp odor, also called nitrogen(IV) oxide.

Question 37

How can ammonium compounds be tested?

Answer 37

Add NaOH and heat. Ammonia gas is released, turning damp red litmus paper blue.

Question 38

How can nitrate(V) ions be tested?

Answer 38

Heat with NaOH and Devarda’s alloy. Ammonia gas is produced, indicating the presence of nitrate(V) ions.

Question 39

What are the key steps of the nitrogen cycle?

Answer 39

N2 + H2 → NH3 → NH4⁺ → NO2⁻ → NO3⁻ → N2, involving reactions with oxygen, hydrogen, and electrons.