Factors Affecting Reaction Rates

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Reaction Rate Noun

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[ree-ak-shun rayt]

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Reaction Rate

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The measure of the speed at which reactants are converted into products during a chemical reaction over time.

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Example: This graph shows that as a chemical reaction proceeds over time, the amount of starting materials (reagents) decreases while the amount of new substances (products) increases.

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Collision Theory Noun

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[kuh-lizh-un thee-uh-ree]

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Collision Theory

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A model explaining that chemical reactions occur when reactant particles collide with sufficient energy and correct orientation.

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Example: For a chemical reaction to happen, molecules must collide in the correct orientation, not just bump into each other any which way.

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Activation Energy Noun

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[ak-tuh-vay-shun en-er-jee]

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Activation Energy

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The minimum amount of energy that reacting particles must possess for a chemical reaction to occur upon collision.

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Example: This image shows particles colliding. The bright flash in the center represents a collision with enough energy—the activation energy—to start a chemical reaction.

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Concentration Noun

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[kon-sen-tray-shun]

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Concentration

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The amount of a substance, or solute, present in a given quantity of a solution or specific volume.

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Example: This image shows that concentration is the amount of a substance in a given volume. The beakers on the left have a higher concentration (more purple substance) than the beakers on the right.

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Surface Area Noun

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[sur-fis air-ee-uh]

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Surface Area

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The total measure of the exposed surface of a solid reactant available for interaction in a chemical reaction.

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Example: This image compares two reactions. Breaking a substance into smaller pieces (right beaker) increases its surface area, allowing more particles to react at once.

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Catalyst Noun

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[kat-l-ist]

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Catalyst

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A substance that increases the rate of a chemical reaction by lowering the activation energy without being consumed.

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Example: A catalytic converter uses a catalyst to speed up the conversion of harmful car exhaust gases into less harmful substances like carbon dioxide and water.

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Inhibitor Noun

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[in-hib-i-ter]

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Inhibitor

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A substance that slows down or prevents a chemical reaction, often by increasing activation energy or blocking catalysts.

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Example: An inhibitor molecule blocks the active site of an enzyme, preventing the substrate from binding and stopping the chemical reaction from happening.

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Enzyme Noun

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[en-zahym]

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Enzyme

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A biological catalyst, typically a protein, that speeds up biochemical reactions necessary for life at normal body temperatures.

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Example: An enzyme has a specific active site that binds to substrates, forming a product. The enzyme is unchanged and can be reused, speeding up the reaction.

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Homogeneous Catalyst Noun

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[hoh-muh-jee-nee-uhs kat-l-ist]

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Homogeneous Catalyst

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A catalyst that exists in the same physical state (solid, liquid, or gas) as the reactants it catalyzes.

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Example: A catalyst (blue sphere) mixes with reactants (yellow and green) in the same phase, providing a new reaction path with a lower energy barrier (hill).

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Heterogeneous Catalyst Noun

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[het-er-uh-jee-nee-uhs kat-l-ist]

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Heterogeneous Catalyst

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A catalyst that exists in a different physical state from the reactants of the chemical reaction it catalyzes.

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Example: A catalytic converter uses a solid catalyst (honeycomb structure) to speed up reactions that clean harmful gases (dirty emissions), demonstrating a heterogeneous catalyst.