Rate of reaction(f5)

A reaction is fast , the time taken for the reaction is short . A reaction is slow , the time taken for the reaction is long . The rate of reaction depends to the speed of reaction . If a reaction is fast, its rate of reaction is high . If a reaction is slow , its rate of reaction is low . The rate of reaction is inversely proportional (berkadar songsang ) with time . Rate ά 1 time taken for reaction Rate of reaction = change in quantity of product / reactant time taken For gas product , rate of reaction = volume of gas time From a graph , the average rate of reaction = the gradient ( kecerunan) of graph

Determine the rate of reaction Average rate of reaction Rate of reaction at a given time ( pada masa tertentu ) Example (a) : Average rate of reaction = change in amount of reactant or product time taken Example : reactant Product CaCO 3 + 2HCl CaCl 2 + H 2 O + CO 2 If 20 cm 3 of carbon dioxide, CO 2 is released in 10 seconds for the above reaction, therefore, the average rate of reaction can be calculate as : Average rate of reaction = total volume of gas released = 20 cm 3 = 2cm 3 s - total time taken 10s CaCO 3 + 2HCl CaCl 2 + H 2 O + CO 2

Example (b) : The graph below shows the volume of carbon dioxide ,CO 2 released against time for the reaction between calcium carbonate , CaCO 3 and dilute hydrochloric acid, HCl . Determine the rate of reaction at the 20 th second. Rate of reaction at the 20 th second = p q = ( 60 - 30 ) cm 3 ( 40 - 0 ) s = 0.75 cm 3 s - 10 20 30 40 50 60 70 80 10 20 30 40 50 60 Volume of gas / cm 3 Time / s p q P = 60 - 30 Q = 40 - 0 0

The rate of reaction decreases with time bacause :- the concentration of a solution is decreasing as time . Mass of reactant is decreasing as time . The steeper (semakin curam) the gradient of the graph ,the higher the rate of reaction . The gradient of the graph is zero . The rate of reaction at time t 3 is zero (the reaction has stopped ). t 3 Volume of gas Time

Example 1 Mg + 2HCl MgCl 2 + H 2 Determine the Average rate of reaction at 50 seconds. Rate of reaction at 55 seconds . Maximum number of moles of gas released . Concentration of hydrochloric acid . Mass of magnesium that reacted . ( Relative atomic mass ; Mg = 24 . Molar volume : 24 dm 3 mol -1 at room condition . ) The graph shows the change in volume of gas with time for the reaction between excess magnesium and 25 cm 3 of hydrochloric acid . 50 360 Maximum volume of gas Time /s Volume of gas / cm 3

Solution Average rate of reaction in 50 seconds = 360 = 7.2 cm 3 s -1 50 (b) Rate of reaction at 55 seconds = 0 cm 3 s -1 (zero ) © From the graph, the maximum volume of gas released is 360 cm 3 . The maximum number of moles of volumes of gas released = volume of gas = 360 molar volume 24000 = 0.015 mol (d) Mg + 2HCl MgCl 2 + H 2 V = 25 cm 3 , M = ? 1 mol of H 2 gas produced by 2 mol of HCl 0.015 mol of H produced by 0.015 X 2 mol of HCl = 0.03 mol of HCl The number of moles of HCl = MV / 1000 M = 0.03 X 1000 = 1.2 mol dm -3 25

(e) Mg + 2HCl MgCl 2 + H 2 Mass =? 1 mol of H 2 produced by 1 mol of Mg 0.015 mol of H 2 produced by 0.015 mol of Mg The number of moles of Mg = mass / RAM 0.015 = mass 24 Mass of Mg = 0.015 X 24 = 0.36 g 2 . 6.5 g of zinc powder was mixed with dilute nitric acid , HNO 3 in excess. It was found that it took 50 seconds for all the gas produced to be collected . Calculate the average rate of reaction in cm 3 s -1 . ( Relative atomic mass : Zn ,65 : Molar volume : 24 dm 3 mol -1 at room condition ) Ans : 48 cm 3 s -1

CATALYST Temperature CONCENTRATION Pressure Surface Area

Size of the particles / Surface area The smaller the size of particles ,the larger the total surface area , the rate of reaction will be higher . Small total surface area Large total surface area CONCENTRATION The higher the concentration of a reactant ,it have more particles per unit volume . The rate of reaction will be higher. A shorter time is required to complete the reaction .

Temperature The higher the temperature of the reaction, the particles obtain more kinetic energy . Therefore ,the rate of reaction will be higher . catalyst A catalyst will change the rate of reaction . A catalyst only changes the rate of reaction but not the quantity of products. A catalyst does not undergo any chemical change at the end of the reaction . Pressure Pressure can affect the rate of reaction only if it involves gases. A higher pressure can increase the rate of reaction . The increase of pressure will compress the gas. The particles of a gas will collide more frequently when in a compressed state (smaller volume).

To study the effect of the size of reactant on the rate of reaction. From graph :- The rate of reaction between the small marble chips and dilute hydrochloric acid is higher compared to the rate of reaction between the large marble chips and dilute hydrochloric acid. The smaller the size of the reactant, the higher the rate of reaction . A smaller reactant size has a larger total exposed surface area. The rate of reaction for both experiments decreases with time because :- the mass of marble becomes decreases the size of marble chips becomes decreases the concentration of hydrochloric acid becomes decrease . Maximum volume of gas in both experiments at the end of the reaction is the same because the volume , concentration and the mass of marble used in both experiments are the same . Volume of gas Time Marble powder marble pieces

From graph (a): It takes a longer time to form the sulphur precipitate if the concentration of sodium thiosulphate is low . It takes a shorter time to form the sulphur precipitate when the concentration of sodium thiosulphate is high . From graph (b), the rate of reaction is high when the concentration of sodium thiosulphate is high . the concentration of sodium thiosulphate solution is directly proportional to 1/time or rate of reaction . The effect of concentration Ionic equation : S 2 O 3 2- + 2H +1 H 2 O + SO 2 + S

Effect of temperature From a graph (a):- A shorter time is needed for sulphur to precipitate at a higher temperature. A longer time is needed for sulphur to precipitate at a lower temperature . From a graph (b) : The rate of reaction will increase when the temperature of the reactant increases . The rate of reaction doubles each time the temperature increases by 10 0 C .

Effect of The rate of decomposition of hydrogen peroxide can be increased by increasing the amount of catalyst . The rate of decomposition of hydrogen peroxide decreases with time because the concentration of hydrogen peroxide is decrease when the time increases . Maximum volume of gas in both experiments at the end of the reaction is the same because the volume and concentration of hydrogen peroxide solution used in both experiments are the same . catalyst Hydrogen peroxide H 2 O 2 , decomposes at a faster rate of reaction after the presence of the catalyst ,manganese (IV) oxide, MnO 2 to release oxygen O 2 gas. 2H 2 O 2 2H 2 O + O 2

COLLISION THEORY ( TEORI PERLANGGARAN)

Collision theory states that before any chemical reactions can occur, particles of the reactants have to collide with each other . Effective collision ---- collision that produces chemical reactions by achieving the minimum energy and correct collision orientation . Colliding particles must have equal or be more than the activation energy ( tenaga pengaktifan ) . Activation energy is the minimum energy needed by the reactant particles to react . Correct collision orientation Effective collision Reaction happens H H I I I I H H I H I H

Energy released to its surroundings causes the total energy of the products formed to be lower than the total energy of its reactants. EXOTHERMIC REACTION Release of heat Energy Products reactants Activation energy E a

ENDOTHERMIC REACTION Energy is absorbed from its surroundings causes the total energy of the products formed to be higher than the total energy of its reactants Absorption of heat ENERGY PRODUCTS REACTANTS Activation energy E a

(i) Collision frequency (the number of collision in one second). The rate of reaction depends on : If the number or frequency of collisions is high, the number of collisions that occur is high . The frequency of effective collisions also increase, therefore the rate of reaction becomes higher . (ii) Magnitude of activation energy . Activation energy increases , the number of collisions for a reactant particles can achieved high activation energy. The number of effective collisions is small. The rate of reaction will decrease .

The effect of the surface area The rate of reaction increases when the size of the particles is smaller . The total surface area that is exposed to collision between particles are larger . The collision frequency will increase. Caused the effective collision frequency will increase . The rate of reaction also increases. Less collision between particles More collision between particles

CONCENTRATION The rate of reaction increases if the concentration of a reactant is increase . A higher concentration of the solution increases, the number of particles per unit volume also increases. Can caused the frequency of collisions increase . Thus, the frequency of effective collisions will increase. Therefore , the rate of reaction increases . Less collision between particles More collision between particles Particles

Temperature When the temperature of the reactant is increased , the rate of reaction increase too . because the kinetic energy of particles increase. The particles of the reactant move faster . The number of particles which achieved activation energy also increases. The frequency of collisions between particles also increases . The effective collision frequency between the particles increases . The rate of reaction will increase too .

CATALYST Can increase the rate of reaction by lowering activation energy of a reaction . Provides an alternative pathway ( lintasan alternatif ) that requires a lower activation energy . More particles will have effective collision that has a lower activation energy . The frequency of effective collisions increase . The rate of reactionj will increase too. E a : Activation energy without catalyst E b : Activation energy with catalyst . Alternative pathway MnO 2 Fe Platinum( Pt ) V 2 O 5 E a E b Energy

PRESSURE Influences the rate reactions involving gas reactants / product. pressure increases when the volume of the gases is reduced . collision frequency between particles increases which caused the frequency of effective collisions increases too . more particles have activation energy . thus , the rate of reaction increases . APPLICATION Keeping food in the refrigerator Burning of fuels Cooking food with pressure cookers Cooking food with small pieces will get cooked faster . Use of catalyst in industry .

vanadium(v) oksida - catalyst The raw materials --- sulphur and air Sulphur is burnt in air , sulfur dioksida terhasil S + 0 2 S0 2 Sulfur is oxidised to sulfur dioxide sulphur dioxide is mixed with dry oxygen is passed over vanadium (V) oxide, (catalyst) at a temperature of 450 – 500 0 C and a pressure of 1 Atmosphere (atm ) Sulphur trioxide gas is dissolved in concentrated sulphuric acid to produce oleum SO 3 + H 2 SO 4 H 2 S 2 O 7 (oleum) Oleum is diluted with an equal volume of water To produced concentrated sulphuric acid . H 2 S 2 O 7 + H 2 O 2H 2 SO 4 Production of Sulphuric Acid

Ammonia is oxidised to nitrogen monoxide by oxygen. The presence of platinum ( catalyst ). Temperature 850 0 – 900 0 C & pressure 5 atm. 4NH 3 + 5O 2 4NO + 6H 2 0 Nitrogen dioxide is dissolved in water to produce nitric acid . 4NO 2 + O 2 + 2H 2 O 4HNO 3 Nitrogen monoxide is oxidised to nitrogen dioxide 2NO + O 2 2NO 2 Production of Nitric Acid

Gas hidrogen dan nitrogen bertindak balas pada suhu 450 0 - 550 0 C , tekanan 200 – 500 atm dan dibantu oleh mangkin ( serbuk ferum ) Bahan penggalak ialah molibdenum N 2 + 3H 2 2NH 3 Production of Ammonia

Rate of reaction(f5)

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