# Rates

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Education

Published on May 14, 2010

Author: kwarne

Source: slideshare.net

## Description

A set of slides created to teach Rates to learners at Bishops Diocesan College in Cape Town.

Rates of Reaction Keith Warne

Bond Energies H H H H O H O O H H + O O H H O H H H Energy given out Energy taken in 2H2 + O2 2H2O• Energy is ………………….to break bonds E breaking = 2 x E(H-H) +1x (O=O) =• Energy ………………………when new bonds formed E forming = 4 x (H-O)=• Total energy change ΔH = E…………….. (Reactant)+ Ef…………………(prod) (-)

Energy Changes During Reactions The heat energy or Enthalpy (H) changes in a reaction are related to the BREAKING and FORMING of chemical bonds. Energy is TAKEN IN when bonds break and RELEASED when bonds form. The MINIMUM ENERGY REQUIRED to start the reaction is called the ACTIVATION ENERGY. (Ea) Activated complex Ea = Hbreaking Ea = Hbreaking Hforming HformingPotential Energy Potential Energy E react E prod Energy Energy taken in given off E prod E react ΔHr > 0 (+) ΔHr < 0 (-) ENDOTHERMIC EXOTHERMIC The overall energy change for the reaction can be found by using either of the two equations below: ΔHr = Eprod – EReact = Hbreaking–Hforming

Reactant Concentration (/mol.dm-3) FAST SLOWTime /(s) STOPPED Product Concentration (/mol.dm-3) FAST Rate Graphs SLOWTime /(s) STOPPED

Factors Affecting Rate• Surface area - solids only - greater area …….. effective collisions. 2a Dividing a a solid into smaller 4xa 4xa pieces 4x2a ………..…. the surface 4xa 4xa area. (Perimeter) Total perimeter Total perimeter 16a 8a

Energy Distribution of Particles Number of Particles Energy Ea• Higher temperature: increases the spread of energies.• More particles have enough energy to react.• REACTION RATE INCREASES!

CatalystsA catalyst is a substance, which can alter the ………. of a reaction without being permanently ………………………at the end of it.Catalyst - affects number of effective collisions. a) a small amount of catalyst can produce a ……………..amount of chemical change. b) catalysts remain unchanged chemically, but they can change physically c) catalysts are very …………….to particular reactions.

EXAM QUESTIONS Nov 2010

Keith Warne• This is a SAMPLE presentation only• The full presentations contain loads more slides (20-100) and are available on the click2learn website here• http://www.click2learn.co.za/shop/lessoncloud-grade-12-science-slides/ (paste into your browser if link above does not work)• I have other resources available from my Science Café site feel free to have a lookSAMPLE ONLY SAMPLE ONLY

Keith Warne• This is a SAMPLE presentation only• The full presentations contain loads more slides (20-100) and are available on the click2learn website here• http://www.click2learn.co.za/shop/lessoncloud-grade-12-science-slides/ (paste into your browser if link above does not work)• I have other resources available from my Science Café site feel free to have a lookSAMPLE ONLY SAMPLE ONLY

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