An athlete “burning” calories 7.4 Reaction Rates Key Concepts What does a reaction rate tell you? What factors cause reaction rates to change? An athlete “burning” calories

A much ____________ way of releasing the energy is to burn The banana in the photo is providing the cyclist with about 100 ___________ of energy. The energy from the banana is _____________ during a series of chemical reactions that occur inside your ___________. A much ____________ way of releasing the energy is to burn the banana ___________ the body during a combustion reaction Calories released body faster outside

Reactions Over Time The progress of any chemical reaction can be measured over ________ A reaction ________ is the rate at which reactants change into ______________ over time Reaction rates tell you how ________ a reaction is going time rate products fast

Factors that affect reaction rate include… __________________ Activation Energy Temperature Surface Area Stirring Concentration Catalysts

Activation Energy For a reaction to occur between two substances, particles of those substances must ___________ with enough _______ to cause a change to take place The amount of energy needed when the particles collide is called _____________ _____________ It is kind of like a small _______ that all reactions need For example, ____________ and ___________ molecules can react to produce ___________ and large amounts of ______________ 2H2 + O2 2H2O + energy collide force activation energy “push” hydrogen oxygen small water

2H2 + O2 2H2O + energy Oxygen and hydrogen gas, however, can exist in the same container for ________ without reacting The reaction will not begin until enough activation _________ is provided to start the reaction years energy

Temperature Most reactions go faster at __________ temperatures because an increase in temperature… increases the ____________ of particles Increases their likelihood of ____________ Example… Food _________ quickly at higher temperatures but remains fresh longer when _________ or _______________ higher speed colliding spoils cold frozen

Surface Area The ______________ the particle size of a given mass, the _____________ is its surface area. Think of a newspaper…will a newspaper cover more area folded together OR as separate smaller sheets? smaller larger as separate, smaller sheets

The rate of combustion was very ____________ due to the small Increased surface area increases ________________ that involve reacting particles. This fire was a combustion reaction between grain ___________ and oxygen. The rate of combustion was very ____________ due to the small particle size of the grain dust. collisions dust rapid

Which picture below shows a higher concentration of particles? The ____________ of substance present in a certain ___________ is called the concentration of the substance Which picture below shows a higher concentration of particles? amount volume 5 particles 10 particles 10 particles

Increasing the concentration of a __________ will speed up a reaction because the particles are _________ together and will ___________ more often reactant closer collide

Stirring reactants increases their _________________ to each other. In a washing machine, particles of detergent react with particles of the _____________ on clothes. A washing machine ____________ up the reaction by stirring the contents back and forth. exposure stains speeds

In a chemical equation, a catalyst may be written… Catalysts A catalyst is a substance that ________ up the rate of a reaction without being _______ or _______ up by the reaction In a chemical equation, a catalyst may be written… _________ the arrow 2H2O2  2H2O + O2 or before ____ after an arrow to show that it has not changed 2H2O2 + MnO2  2H2O + O2 + MnO2 speeds changed used above More common! MnO2 and

A catalyst speeds up a chemical reaction by ___________ the activation energy needed to start the reaction lowering

Why is reaction rate important? Chemical engineers and industries wish to produce their products ______________ The faster the rate, the ______ product that can be made Food scientists are also interested in ________ down the reactions that cause food to spoil efficiently more slowing

Review Question 1 What is activation energy? The energy required to start a reaction

Review Question 2 Predict how the following factors will affect the rate of a reaction… Increasing temperature Decreasing concentration Adding a catalyst Stirring two substances Speed up Slow down Speed up Speed up