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Chemistry 18.1
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Rates of Reaction
The heat given off by the corrosion reaction of an iron-magnesium alloy with salt water can produce a hot meal. The rate of reaction is increased by adding salt water, so heat is produced rapidly. You will learn some ways in which the rate of a reaction can be increased.
18.1
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Rates of Reaction >
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Collision Theory
Collision Theory
How is the rate of a chemical change expressed?
18.1
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Rates of Reaction >
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18.1 Collision Theory
In chemistry, the rate of chemical change, or the reaction rate, is usually expressed as the amount of reactant changing per unit time.
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>Rates of Reaction18.1 Collision Theory
A rate is a measure of the speed of any change that occurs within an interval of time.
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>Rates of Reaction
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Collision Theory
Rates of chemical reactions are often measured as a change in the number of moles during an interval of time.
18.1
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>Rates of Reaction Collision Theory
According to collision theory, atoms, ions, and molecules can react to form products when they collide with one another, provided that the colliding particles have enough kinetic energy.
18.1
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>Rates of Reaction
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Collision Theory
Effective Collision
18.1
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>Rates of Reaction
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Collision Theory
Ineffective Collision
18.1
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>Rates of Reaction Collision Theory
The minimum energy that colliding particles must have in order to react is called the activation energy.
18.1
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>Rates of Reaction Collision Theory
An activated complex is an unstable arrangement of atoms that forms momentarily at the peak of the activation-energy barrier.
The activated complex is sometimes called the transition state.
18.1
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Rates of Reaction >
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Factors Affecting Reaction Rates
Factors Affecting Reaction Rates
What four factors influence the rate of a chemical reaction?
18.1
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Rates of Reaction >
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Factors Affecting Reaction Rates
The rate of a chemical reaction depends upon temperature, concentration, particle size, and the use of a catalyst.
18.1
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Rates of Reaction >
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Factors Affecting Reaction Rates
Animation 22
Explore several factors that control the speed of a reaction.
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>Rates of Reaction Factors Affecting Reaction Rates
Temperature
Storing foods in a refrigerator keeps them fresh longer. Low temperatures slow microbial action.
18.1
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>Rates of Reaction Factors Affecting Reaction Rates
Concentration
a. In air, a lighted splint glows and soon goes out.
b. When placed in pure oxygen (higher oxygen concentration), the splint bursts into flame.
18.1
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>Rates of Reaction Factors Affecting Reaction Rates
Particle Size
The minute size of the reactant particles (grain dust), and the mixture of the grain dust with oxygen in the air caused the reaction to be explosive, destroying the grain elevator.
18.1
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>Rates of Reaction Factors Affecting Reaction Rates
Catalysts
18.1
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Rates of Reaction >
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Factors Affecting Reaction Rates
Simulation 23
Explore the effects of concentration, temperature, and a catalyst on reaction rate.
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>Rates of Reaction Factors Affecting Reaction Rates
An inhibitor is a substance that interferes with the action of a catalyst. Antioxidants and antimicrobials used in drying fruits and preserving fruit juices slow the action of microbes and limit contact with air.
18.1
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Section Quiz
-or-Continue to: Launch:
Assess students’ understanding of the concepts in Section
18.1 Section Quiz.
18.1.
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18.1 Section Quiz.
1. The units below that would be appropriate to measure the rate of a chemical reaction is
a. mmol/s.
b. mol/L.
c. kJ/mol.
d. h/mol.
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18.1 Section Quiz.
2. In a chemical reaction, the energy of reactants is always
a. greater than the energy of the products.
b. more than the activation energy.
c. less than the activation energy.
d. less than the energy of the products.
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18.1 Section Quiz.
3. An increase in which one of the following will NOT increase the reaction rate?
a. temperature
b. concentration of reactants
c. total mass of reactants
d. surface area of reactants
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18.1 Section Quiz.
4. A catalyst works because it
a. lowers the activation energy.
b. increases the temperature.
c. is permanently changed in a reaction.
d. supplies energy to a reaction.
END OF SHOW