Topic 8

Chemical Reaction Rates  Chemical reactions can occur at different speeds. Why does one reaction take longer than another? Can you speed up or slow down reactions?

Four ways to Speed up Reactions  Increase Temperature  Increase Surface Area  Increase Concentration  Add a catalyst  o6zm_kM o6zm_kM  up-chemical-reactions-and-get-a-date up-chemical-reactions-and-get-a-date

Temperature  Increasing the temperature increases the rate of reaction Why? At higher temperatures, molecules move faster and collide more frequently. Therefore, new substances can be formed more quickly.  Example: Cooking The amount of chemical reactions in the liquid batter are increased with higher temperatures.  Example: Preserving Fruit Fresh fruit and vegetables are often kept in the fridge to slow down the chemical reactions

Surface Area  Crushing materials increases the amount of surface area that is available to react. A powder of a substance will react much more quickly than a block of the same substance. Zg&feature=related Zg&feature=related bHYg bHYg

Concentration  Increasing the amount of substance per unit of volume increases the amount of substance that is available to react. If you are doing a lab with acid, a more concentrated acid will react faster than a dilute concentration.

Catalysts  What is a catalyst? A substance that speeds up the rate of a reaction without being changed itself. A catalyst increases the speed of the reaction – it doesn’t interfere with the products being created  Natural catalysts are called enzymes Saliva is called salivary amylase – it breaks apart your food to aid in digestion An enzyme in your tears attacks the cell wall of the bacteria to prevent an infection. ture=related ture=related

Inhibitors  Inhibitors are substances that slow down chemical reactions.  Examples: Plants have inhibitors to stop germination until conditions are right Foods and medicines have inhibitors in them to prevent decomposition Hydrogen Peroxide has inhibitors in it to prevent its molecules from decomposing too quickly

Corrosion  Corrosion is the oxidation of metals or rocks in the presence of air and moisture.  The most common type of corrosion: Rust  oAdk038mIQ&feature=related oAdk038mIQ&feature=related

Preventing Corrosion  Corroded materials lose their strength. Once materials lose the top layer, oxygen from the air can reach the inner layers.  Prevention? Apply a thin coat of paint Coat it with a thin layer of zinc – this process is called galvanization  Examples? Galvanized nails so that job sites aren’t ruined Chromium covered car parts to protect the lead  Reminder: What is the electrochemical process to coat a metal with another type of metal? Electroplating

Combustion  The highly exothermic combination of a substance with oxygen.  Every time something burns, it combines with oxygen from the air.  Even the food you eat is converted to energy by combining with the oxygen you breathe.

Products of Combustion  The products of burning a hydrocarbon (hydrogen and carbon) are always the same   Products: CO 2(g) and H 2 O (g) and heat CH 4(g) + 2O 2(g)  CO 2(g) + 2H 2 O (g) + heat C 2 H 8(g) + 5O 2(g)  3CO 2(g) + 4H 2 O (g) + heat

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