By: Nikki Snider & Seth Damouth(:

Reactions Over Time

Progress of any chemical reaction can be measured over time. Different reactions have different durations. Some reactions happen instantly, while other reactions happen gradually.

Example of Reaction that happens instantly: explosion of TNT. Example of a reaction that happens gradually: tree leaves changing color during autumn.

Factors affecting reaction rates would be: Temperature, surface area, stirring, concentration, and catalysts.

TEMPERATURE! Temperature affects reaction time because the increase in temperature increases the reaction and a decrease in temperature will decrease the reaction rate.

o Increasing the temperature of a substance causes its particles to move faster on average. o Particles that move faster are both more likely to collide and more likely to react. If the number of collisions that produce reactions increases, then the reaction rate increases.

Examples of temperature affecting reaction rates.. If you cook an egg in a frying pan and you increase the temperature of the stove, the egg will cook faster. If you store milk in a refrigerator to slow down the reaction rate, it will slow down the time but it wont stop it completely. It would eventually spoil, but the rate of spoiling decreases if milk is kept cold.

Surface Area! The smaller the particle size of a given mass, the larger its surface area.

Example: Using a newspaper to cover a floor of a room. If you keep all the sections folded together you can only cover a small amount of the floor. When you unfold them, lay them on the floor like tiles, you are able to cover more of the floor. That allows you to cover more with the same amount of mass.

An increase in surface area increases the exposure of reactants to one another. The greater the exposure, the more collisions there are that involve reacting particles. More collisions, more particles will react. This is why increasing the surface area of a reactant tends to increase the reaction rate.

This grain elevator exploded when grain dust reacted with oxygen in the air.

Stirring! Stirring the reactions will generally increase the reaction rate. Collisions between the particles are more than likely to happen.

Example of how stirring affects reaction rates.. When you wash your clothes in a washing machine, particles of detergent react with particles of the stains on your clothes. This reaction would go slowly if the clothes sat in a tub of water with the detergent. A washing machine speeds up the reaction by stirring the contents back and forth.

Concentration! Concentration refers to the number of particles in a given volume. The more reacting particles that are present in a given volume, the more opportunities there are for collisions involving those particles.

For gasses, concentration changes with pressure. The greater the pressure of a gaseous reactant, the greater its concentration, and the faster the reaction rate.

Catalysts! A catalyst is a substance that affects the reaction rate without being used up in the reaction. Chemist use catalyst to speed up a reaction or enable a reaction to occur at a lower temperature.

QUIZ!(: 1.) What factors affect reaction rates? A. Temperature and surface area. B. Stirring and Concentration. C. Catalysts. D. All of the above. 2.) True or False? Different reactions have different durations. 3.) How does stirring affect reaction rates? 4.) True or False? TNT is a example that happens instantly. instantly.

5.) Fill in the blank: The more ______, the more particles will react. A. Collisions. B. Gasses. C. Catalysts. 6.) What’s a catalysts? 7.) How does temperature affect reaction rates? 8.) True or False? Concentration refers to the number of particles in a given volume. 9.) Give an example of how stirring affects reaction rates. 10.) A tree changing color during autmumn is an example of what? A. Reaction happening gradually. B. Reaction happening