# OCR F334 The Thread of Life

- Created by: Bethany.
- Created on: 13-05-16 20:22

First 512 words of the document:

F334 Chemistry of Materials: The Thread of Life

Kinetics

(a) explain and use the terms:

Rate of reaction Rate of reaction the rate at which reactants are converted into products the change in

concentration of a reactant or product divided by the time taken for the change to occur.

Order of e.g. rate = k [H

2O 2] [catalase]

reaction (both The reaction is first order with respect to H

2O 2 and first order with respect to catalase. The

overall and with reaction is overall second order.

respect to a

+

given reagent) e.g. rate = k [BrO 3] [Br ] [H

]2

The reaction is first order with respect to both BrO 3 and Br , and second order with respect

+

to H .

If you double the concentration of the reactant and the rate stays the same zero order

with respect to the reactant.

If you double the concentration of the reactant and the rate doubles first order with

respect to the reactant.

If you double the concentration of the reactant and the rate quadruples second order

with respect to the reactant.

n

Rate of The general rate equation is: r ate = k[A]m [B] where m and n are the powers to which the

constant, concentration need to be raised they usually have the values of 0, 1 and 2. k is the rate

including units; constant the bigger it is, the faster the reaction. The value of k varies with temperature. m

use empirical + n gives the overall order of the reaction.

rate equations

of the form: Example: The reaction below was found to be second order with respect to NO and zero

3

rate = k[A]m n

[B] order with respect to CO and O 2. The rate is 1.76 x 10

mol dm3

s1 , when [NO] = [CO] = [O 2]

3 3

where m and n = 2.00 x 10 mol dm .

NO + CO + O2 NO 2 + CO

are integers; 2

carry out

1. Write out the rate equation :

calculations 0

Rate = k [NO]2 [CO]0 [O 2]

= k[NO]2

based on the 2. Insert the concentration and rate and rearrange the equation to give k:

rate equation 1.76 x 103

= k x (2.00 x 103

)2

3 3 2

k = 1.76 x 10 / (2.00 x 10 ) = 440

3. Find the units for k by putting the other units in the rate equation:

1 1 1

k = mol dm3 s / (mol dm3

)2 = s / mol dm3 = mol1 dm3 s

1 3 1

Therefore the answer is: k = 440 mol dm s

Overall Order Units for k

1

0 mol dm3 s

1 s1

1

2

mol1 dm3 s

2 6 1

3 mol dm s

Understand According to the rate equation, reaction rate depends only on the rate constant and

that the rate reactant concentrations . Since the reactant concentrations do not change, the rate

constant k constant must change. Therefore, the rate constant, k, increases with increasing

increases with temperature.

increasing

temperature

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