Chemical reactions
57 flashcards covering Chemical reactions for the ACT Science section.
Chemical reactions are processes where substances interact to form new materials with different properties. For example, when wood burns, it combines with oxygen to produce ash, gases, and heat, transforming the original matter. This concept is central to chemistry because it helps explain how atoms rearrange during these changes, following fundamental laws like the conservation of mass. Understanding chemical reactions allows you to predict outcomes in various scenarios, from industrial processes to biological functions.
On the ACT Science section, chemical reactions appear in questions that require interpreting graphs, analyzing experimental data, or identifying reaction types such as synthesis or decomposition. Common traps include mistaking physical changes, like melting, for chemical ones, or overlooking details in data sets that indicate energy shifts. Focus on recognizing key evidence, like color changes or gas formation, and practicing how to balance equations or apply concepts to real-world contexts. For better preparation, always practice identifying reaction types from sample equations.
Terms (57)
- 01
Chemical Reaction
A process where substances are converted into different substances through the breaking and forming of chemical bonds.
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Reactants
The starting substances in a chemical reaction that undergo change to form new products.
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Products
The substances formed as a result of a chemical reaction.
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Balancing Chemical Equations
The process of ensuring the number of atoms of each element is the same on both sides of a chemical equation to obey the law of conservation of mass.
- 05
Conservation of Mass
A law stating that mass is neither created nor destroyed in a chemical reaction, so the total mass of reactants equals the total mass of products.
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Synthesis Reaction
A chemical reaction where two or more substances combine to form a single, more complex substance.
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Decomposition Reaction
A chemical reaction where a single compound breaks down into two or more simpler substances, often due to heat or electricity.
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Single Replacement Reaction
A chemical reaction where one element replaces another element in a compound, resulting in a new element and a new compound.
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Double Replacement Reaction
A chemical reaction where the cations and anions of two different compounds switch places, forming two new compounds.
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Combustion Reaction
A chemical reaction where a substance reacts rapidly with oxygen, producing heat and light, often forming carbon dioxide and water.
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Exothermic Reaction
A chemical reaction that releases energy, usually in the form of heat, making the surroundings warmer.
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Endothermic Reaction
A chemical reaction that absorbs energy, usually from the surroundings, making them cooler.
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Activation Energy
The minimum amount of energy required to start a chemical reaction by breaking the bonds in the reactants.
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Catalyst
A substance that speeds up a chemical reaction without being consumed, by lowering the activation energy.
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Inhibitor
A substance that slows down or prevents a chemical reaction from occurring.
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Reaction Rate
The speed at which reactants are converted into products in a chemical reaction.
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Factors Affecting Reaction Rate
Variables such as temperature, concentration of reactants, surface area, and presence of catalysts that influence how quickly a reaction occurs.
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Concentration
The amount of a substance in a given volume of solution, which affects the reaction rate by increasing collision frequency between particles.
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Temperature
A measure of the average kinetic energy of particles; higher temperatures increase reaction rates by providing more energy for collisions.
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Surface Area
The exposed area of a solid reactant; increasing it allows more collisions, thus speeding up the reaction.
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Chemical Equilibrium
A state in a reversible reaction where the forward and reverse reactions occur at the same rate, so concentrations of reactants and products remain constant.
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Le Chatelier's Principle
A principle that predicts how a system at equilibrium will respond to changes in conditions like concentration, temperature, or pressure to restore equilibrium.
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Reversible Reaction
A chemical reaction that can proceed in both forward and reverse directions, depending on the conditions.
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Acid
A substance that donates hydrogen ions (H+) in water, resulting in a solution with a pH less than 7 and often reacting with bases.
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Base
A substance that accepts hydrogen ions or donates hydroxide ions (OH-), resulting in a solution with a pH greater than 7.
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Neutralization Reaction
A reaction between an acid and a base that produces salt and water, reducing the acidity or basicity of the solution.
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pH Scale
A scale from 0 to 14 that measures the acidity or basicity of a solution, where 7 is neutral, below 7 is acidic, and above 7 is basic.
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Oxidation-Reduction Reaction
A chemical reaction involving the transfer of electrons, where one substance is oxidized (loses electrons) and another is reduced (gains electrons).
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Oxidation
The process in a reaction where a substance loses electrons, often involving an increase in oxidation state.
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Reduction
The process in a reaction where a substance gains electrons, often involving a decrease in oxidation state.
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Oxidation State
A hypothetical charge assigned to an atom in a compound, used to track electron transfer in redox reactions.
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Electrolysis
A process that uses electrical energy to drive a non-spontaneous chemical reaction, often to decompose compounds.
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Stoichiometry
The calculation of quantities in chemical reactions based on the balanced equation, including moles, mass, and volume.
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Mole
The unit used in chemistry to measure the amount of substance, equal to 6.022 × 10^23 particles.
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Avogadro's Number
The number 6.022 × 10^23, which represents the number of particles in one mole of a substance.
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Limiting Reactant
The reactant in a chemical reaction that is completely consumed first, determining the amount of product formed.
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Excess Reactant
A reactant that is not completely used up in a reaction, remaining after the limiting reactant is consumed.
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Theoretical Yield
The maximum amount of product that can be obtained from a reaction based on the limiting reactant, calculated from the balanced equation.
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Actual Yield
The amount of product actually obtained from a reaction, which is often less than the theoretical yield due to side reactions or losses.
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Percent Yield
The ratio of actual yield to theoretical yield, multiplied by 100, to express the efficiency of a reaction.
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Common Trap: Unbalanced Equations
A frequent error where equations are not balanced, leading to incorrect stoichiometry calculations and violating conservation of mass.
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Common Trap: Confusing Reactants and Products
Mistaking which substances are inputs and outputs in a reaction, which can cause errors in predicting outcomes or calculations.
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Formula: Law of Conservation of Mass
In a chemical equation, the total mass of reactants equals the total mass of products, expressed as massin = massout.
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Strategy for Balancing Equations
Start with the most complex molecule, balance elements one by one, and adjust coefficients without changing subscripts to ensure equal atoms on both sides.
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Example: Balancing a Simple Equation
For the reaction of hydrogen and oxygen to form water, 2H2 + O2 → 2H2O balances the equation by ensuring four hydrogen and two oxygen atoms on both sides.
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Energy in Chemical Reactions
The change in energy during a reaction, often measured as enthalpy, which determines if the reaction is exothermic or endothermic.
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Enthalpy Change
The heat absorbed or released in a chemical reaction at constant pressure, denoted as ΔH, with negative values for exothermic reactions.
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Gibbs Free Energy
A thermodynamic quantity that predicts the spontaneity of a reaction, calculated as ΔG = ΔH - TΔS, where a negative ΔG indicates a spontaneous reaction.
- 49
Spontaneous Reaction
A chemical reaction that occurs without external intervention, driven by a negative change in Gibbs free energy.
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Entropy
A measure of disorder or randomness in a system; reactions that increase entropy are more likely to be spontaneous.
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Rate Law
An equation that relates the reaction rate to the concentrations of reactants, typically in the form rate = k [A]^m [B]^n.
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Order of Reaction
The sum of the exponents in the rate law, indicating how the reaction rate depends on reactant concentrations.
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Half-Life
The time required for half of the reactants to be consumed in a reaction, often used for first-order reactions.
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First-Order Reaction
A reaction where the rate is proportional to the concentration of one reactant, so the rate law is rate = k [A].
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Second-Order Reaction
A reaction where the rate is proportional to the square of one reactant's concentration or the product of two, such as rate = k [A]^2.
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Intermediate
A species formed in one step of a multi-step reaction that is consumed in a later step, not appearing in the overall equation.
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Transition State
The highest-energy arrangement of atoms during a reaction, representing the point where reactants are converting to products.