Chemical reactions proceed at various rates. The components that affect reaction prices are:

surface ar area of a heavy reactant concentration or pressure of a reactant temperature nature the the reaction presence/absence of a catalyst.

A change in one or much more of these components may change the price of a reaction. In this lesson, you will define these factors, and also describe and predict their results on reaction rates.

Surface Area

Surface area is the exposed matter of a heavy substance.

Imagine the you space holding a perfect cube the magnesium. The surface area is the sum of the area of all six sides the the cube. The surface area the the cube can be enhanced by separating the cube right into smaller cubes. Surface ar area is maximized when a single huge cube is crushed to fine powder.

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The rate of reaction the a solid problem is regarded its surface ar area. In a reaction between a solid and also an aqueous/liquid/gas species, boosting the surface ar area the the solid-phase reactant rises the number of collisions per second and because of this increases the reaction rate.

In a reaction in between magnesium metal and hydrochloric acid, magnesium atoms have to collide through the hydrogen ions. Once the magnesium atoms type one large lump...


however, ...


the variety of collisions per second between magnesium and hydrogen is higher, and the rate of reaction is faster.

Increasing the surface area the a solid reactant rises the reaction rate.

By raising surface area, there are much more collisions every unit the time. That"s why plenty of solids are powdered using a mortar and also pestle prior to being supplied in a reaction.

Examples of other reactions where surface ar area is important are:

active metals through acids, e.g. HCl with zinc charcoal dust v oxygen gas serial dust with oxygen gas


The concentration of a substance deserve to be expressed in a range of ways depending on the nature that a substance. Aqueous solutions frequently have their concentrations to express in mol/L. Because that example, a systems made by dissolving sodium hydroxide in water has its concentration expressed as moles that NaOH per litre the solution. Gases can likewise have your concentrations express in mol/L.

In terms of the collision theory, increasing the concentration of a reactant boosts in the number of collisions between the reacting types per second and thus increases the reaction rate.

Consider the reaction in between hydrochloric acid and also zinc metal.



In one beaker, 6.00 mol/L HCl is reacted v 2.00 g the Zn.

In another,1.00 mol/L HCl is reacted v 2.00 g that Zn.

Which reaction should occur at the much faster rate?

In terms of the collision theory, collisions in between zinc atoms and hydrochloric acid are an ext frequent in the beaker containing6.0 M HCl - there is more acid every unit the volume.


You can adjust the concentration of one aqueous types by just adding more solute (to make it more concentrated) or adding more solvent (to do it more dilute).

You can adjust the concentration of a gas through adding much more gas to a fixed volume or by diminish the volume of the container. Whereas the concentration of a gas have the right to be reduced by removed (evacuating) a gas native a solved volume or by raising the volume that the container.


The concentration the a gas is a function of the pressure on the gas. Raising the press of a gas is specifically the exact same as raising its concentration. If you have a certain variety of gas molecules, you have the right to increase the push by forcing them into a smaller volume.


Under greater pressure or at a higher concentration, gas molecule collide more frequently and also react at a quicker rate. Conversely, increasing the volume of a gas decreases push which consequently decreases the collision frequency and thus reduces the reaction rate.

It is crucial to note yet that there room reactions including gases in which a pressure change does not impact the reaction rate. For this reason, the prices of reactions entailing gases have to be identified by experiment.

Also keep in mind that solids and liquids room not affected by press changes.

Need a good analogy because that the impact of concentration on the rate of a chemical reaction?


With the exemption of some precipitation reactions involving ionic compound in solution, just around all chemical reactions take ar at a quicker rate at higher temperatures. The inquiry is why?

Temperature (in Kelvin degrees) is proportional to the kinetic power of the corpuscle in a substance. For example, if the Kelvin temperature that a problem is doubled, then the typical kinetic power of the particles in that substance is doubled.

At greater temperatures, particles collide an ext frequently and with greater intensity.

Here"s one analogy.

Imagine the you space baby-sitting a bunch the 6 year olds. You put them in a yard and you permit them operation around. Every now and also then a couple of youngsters will run into each other. Now imagine the you decision to feeding them part sugar. What happens? castle run about faster and also of food there room many an ext collisions. Not only that, the collisions are likely to be a lot harder/more intense.

Now, let"s look in ~ the effect graphically. Recall that in any kind of sample of matter (the example we provided previously to be a gas), individual particles have different kinetic energies. Some are moving quick some are moving slowly, and most are relocating at some intermediate speed.


Increasing the temperature by speak 10°C reasons some the the intermediate rate molecules to relocate faster. The result is much more molecules with adequate kinetic energy to type an activated facility upon collision!

Now think about the relationship between threshold kinetic energy and activation energy. Threshold kinetic energy is the minimum quantity of energy required because that colliding particles to reaction - that is the indistinguishable of activation energy or the minimum potential energy gain compelled to kind an set off complex.

As you deserve to see ~ above the graph, a little increase in temperature can twin the variety of molecules through the threshold kinetic energy.


Thus there space two effects of boosting temperature: higher collision soot and more frequent collisions.

A general rule is that a 10°C temperature increase can double a reaction rate. It transforms out the the boost in the reaction rate is mainly a function of the more intense collisions. Increased collision frequency is not as far-ranging a factor.

Nature that Reactants

Individual properties of building materials also impact reaction rates. The border of these properties is broad and there are couple of generalizations that you can apply consistently. Few of the properties in this group are state of matter, molecular size, bond type and bond strength.

State the Matter

Gases tend to react faster than solids or liquids: the takes power to different particles from each other. In order come burn candle wax, the hard wax has to be melted and then vaporized prior to it reacts v oxygen. Methane gas is already in the gas state so the burns faster than wax.



Aqueous ions often tend to react quicker than species in other states that matter: solid lead(II) nitrate will certainly react v solid potassium iodide, however the reaction is really, yes, really slow. That"s because the ionic bonding in each reactant is solid and the ion in each link are hard to separate from each other. As soon as aqueous solutions of this compounds space mixed, the formation of lead(II) iodide is rapid. In aqueous solutions, the ion of each compound are dissociated. When the two the options are blended together, all that is required for a reaction to take place is contact in between the lead(II) ions and also the iodide ions.



Bond kind

Reactions entailing ionic types tend to proceed faster than reactions including molecular compounds.


Bond strength

Reactions entailing the breaking of weaker bond proceed faster than reactions including the break of stronger bonds. Because that example, twin carbon to carbon bonds are stronger than solitary C-C bonds.



variety of Bonds/Molecular Size

Reactions including the break of under bonds every reactant proceed much faster than those involving the break of a larger number of bonds every reactant.


The straightforward ion Fe2+ reacts much faster than oxalate (OOCCOO2-).

Kerosene burns an ext slowly 보다 methane due to the fact that there are more bonds come be broken per molecule the kerosene than there space per molecule of methane. Kerosene is a larger molecule




A catalyst is a types that speeds up a chemical reaction without gift chemically readjusted upon perfect of the reaction. In other words, the massive of a catalyst is the very same before and after a reaction occurs.

Common examples of catalysts include:

MnO2 in the decomposition of H2O2 Fe in the produce of NH3 Pt in the conversion of NO and also CO come N2 and also CO2

Recall the collisions only an outcome in reactions if the particles collide through enough power to get the reactions began (i.e. To get over the activation energy barrier).

Also recall that activation energy corresponds to threshold energy.


Only collisions including particles with adequate kinetic energy result in the development of an caused complex. Corpuscle possessing much less than the threshold power simply bounce apart upon collision.

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The variety of successful collisions every unit that time be increased by lowering the threshold power (or in terms of potential energy, lowering the activation energy).


Adding the appropriate catalyst come a chemical device has exactly this impact on threshold/activation energy.

A catalyst offers an different pathway because that the reaction - a pathway that has actually a reduced activation energy. Be mindful how you speak it.


The catalyzed pathway (shown as a dotted green line above) has actually lower activation energy.

Relating this earlier to the kinetic energy diagram, you view that an ext particles will have enough kinetic energy to react. In various other words, the addition of the catalyst increases the reaction rate.

You"ll explore the effect of a catalyst more on reaction price in the next lesson.


Textbook Readings web page 466: method for measure Reaction rates web page 467: components That affect Reaction price pages 470-471: Collision Theory and ... Concentration, surface Area, Nature the Reactants, and Temperature. Textbook practice Items pages 467-468: item 1, 2, 4, 5, and 6 page 484: item 1 and also 2 pages 486-487: items 1, 2, 3, 4, 5, 6, 9, 12, and also 13 pages 538-541: items 12, 13, 28, 32, 34 and also 35 much more Practice item Why is kindling used to begin a fire in a timber stove? think about this chemical equation:
What effect would increasing the temperature native 25°C to 100°C have on the rate of this reaction? Explain. 10.0 g piece of zinc are included to 1.00 M and also 6.00 M hydrochloric acid remedies at the very same time. Assuming over there is excess mountain in each container, i beg your pardon reaction will proceed faster? Explain. In terms of the result of the nature of reactants on reaction rates, explain the following observations. the reaction between perchloric acid and also iron is quicker than the reaction in between nitrous acid and also iron. sulfur flour reacts gradually with silver, but sulfide ion are promptly precipitated out of systems in a reaction through silver ions. barium reacts through water much more readily 보다 calcium methane burns more rapidly in air than kerosene (C14H30). Cane sugar (sucrose) have the right to be hydrolysed to produce two glucose molecules. This reaction is an extremely slow.
If an mountain is included to the reactants, the reaction price is lot faster. What is the duty of the acid? Explain.

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