Chemistry Grade 10: Chemical Reactions and Energetics

Vocabulary practice flashcards covering Grade 10 chemical reaction rates, collision theory, factors altering reaction velocity, physical versus chemical changes, reaction energetics, enthalpy diagrams, and bond energy calculations.

Rate of Reaction

The increase in concentration of a product species per unit time, or the decrease in the concentration of reactant species per unit time (such as the combustion of oxygen when a fire burns).

Collision Theory

A fundamental theory stating that for a chemical reaction to occur between atoms, ions, or molecules, the reacting particles must collide effectively.

Effective Collision

A collision between reactant particles that successfully results in a reaction to produce one or more products; it requires particles to collide with the correct orientation and with sufficient kinetic energy to overcome the activation energy.

Concentration

The ratio of solute in a solution to either a solvent or the total solution, typically expressed in terms of mass per unit volume.

Five Signs of a Chemical Reaction

The five primary observable indicators confirming a chemical reaction has taken place: light released, temperature change, production of a gas, formation of a precipitate, and color change.

Sodium Thiosulfate and Hydrochloric Acid Reaction

The precipitation reaction represented by the equation $Na_2S_2O_3 + 2HCl \rightarrow 2NaCl + S + SO_2 + H_2O$, whose rate is determined by measuring the time taken for a yellow precipitate of sulfur to form.

Particle Size (Surface Area)

The exposed surface of a solid reactant; breaking a large piece into smaller pieces increases total surface area and the number of reactant particles available, producing more collisions per unit time and a faster reaction rate.

Pressure (in Reaction Rates)

A reaction rate factor applicable to gaseous reactants; decreasing container volume increases system pressure, forcing gas particles closer together and increasing collisions and the proportion of effective collisions per unit time.

Catalyst

A substance that increases the rate of reaction by lowering the required activation energy while remaining chemically unchanged at the end of the reaction.

Enzyme

A specialized protein found in living organisms that functions as a biological catalyst to accelerate organic chemical reactions.

Inhibitor

A substance that reduces or slows down the rate of a chemical reaction.

Temperature (in Reaction Rates)

A property directly proportional to the average kinetic energy of particles; increasing it causes particles to move faster, collide more frequently, and gives a greater proportion of particles kinetic energy exceeding the activation energy.

Photons

Packets of light energy capable of breaking chemical bonds and enabling reactant particles to overcome the activation energy barrier.

Physical Change

A change in state or appearance where the chemical composition remains unaltered (e.g., water molecules remaining identical in both liquid water and solid ice), commonly caused by fluctuations in temperature or pressure.

Chemical Change

A chemical reaction in which substances combine or decompose to produce different substances with new properties, during which chemical bonds are broken and activation change occurs.

Chemical Energetics

The branch of chemistry focused on studying the energy changes that occur during chemical reactions.

Enthalpy ($H$)

The stored energy within chemical bonds, measured as the heat energy that is absorbed to break bonds or released when new bonds form during a chemical change.

Exothermic Reaction

A reaction that releases heat energy into the environment because more energy is released when new product bonds form than is absorbed to break reactant bonds, resulting in a system with lower energy and a negative enthalpy change.

Endothermic Reaction

A reaction that absorbs heat energy from the environment because more energy is absorbed to break reactant bonds than is released when new product bonds form, resulting in a system with higher energy and a positive enthalpy change.

Bond Breaking and Forming Energetics

The fundamental energetic principle that the breaking of bonds is always endothermic (absorbs energy) and the forming of bonds is always exothermic (releases energy).

Change in Enthalpy Formula

The formula used to calculate heat of reaction in kilojoules ($kJ$): $\Delta H = H_{\text{products}} - H_{\text{reactants}}$, where $H_{\text{products}}$ is the energy of products and $H_{\text{reactants}}$ is the energy of reactants.

Bond Energy Calculation Method

A three-step calculation: (1) add reactant bond energies to obtain energy in (absorbed), (2) add product bond energies to obtain energy out (released), and (3) determine $\Delta H = \text{energy in} - \text{energy out}$ in units of $kJ\,mol^{-1}$.