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Burning magnesium ribbon in air Grade 10 SABIS SABIS Chemical

understand that chemical reactions are accompanied by enthalpy changes and these changes can be exothermic (ΔH is negative) or endothermic (ΔH is positive) A Level Chemistry CIE Chemical reactions are accompanied by enthalpy changes, which refer to the heat energy exchanged during the reaction. Enthalpy (H) represents the total energy content of a system, including both internal energy and the energy associated with pressure and volume. By studying enthalpy changes, we gain insights into the energy flow and transformations occurring in chemical reactions. Enthalpy changes can be classified as exothermic or endothermic based on the sign of ΔH, which represents the change in enthalpy. In exothermic reactions, the products have lower enthalpy than the reactants, resulting in a negative ΔH value. This negative ΔH indicates that the reaction releases heat energy to the surroundings. For example, when wood burns, it undergoes an exothermic reaction. The reactants (wood and oxygen) have a higher enthalpy than the products (carbon dioxide, water, and heat), leading to a negative ΔH. The heat released during this reaction warms up the surroundings, making it feel warm and giving off light. On the other hand, endothermic reactions have products with higher enthalpy than the reactants, resulting in a positive ΔH value. This positive ΔH indicates that the reaction absorbs heat energy from the surroundings to proceed. An example of an endothermic reaction is the process of photosynthesis in plants. During photosynthesis, plants convert carbon dioxide and water into glucose and oxygen using energy from sunlight. This reaction requires energy input, which is absorbed from the surroundings, resulting in a positive ΔH. Understanding whether a reaction is exothermic or endothermic is crucial for various applications. It helps us predict the energy changes associated with reactions and understand their impact on the surroundings. Exothermic reactions often have practical applications such as combustion for energy generation, while endothermic reactions are commonly utilized in processes like thermal decomposition or cooling systems. In summary, enthalpy changes in chemical reactions can be exothermic (ΔH is negative) or endothermic (ΔH is positive). Exothermic reactions release heat energy to the surroundings, while endothermic reactions absorb heat energy from the surroundings. By recognizing and understanding these enthalpy changes, we gain insights into the energy dynamics of chemical reactions and their significance in various real-world processes.

< Back Atoms, molecules and stoichiometry This is placeholder text. To change this content, double-click on the element and click Change Content. Chapter Summary Previous Next Learning Outcomes 🎯: Define and use terms such as relative atomic mass, isotopic mass, empirical formula, molecular formula, and the mole in terms of the Avogadro constant. Analyze and use mass spectra to calculate the relative atomic mass of an element. Calculate empirical and molecular formulas using combustion data or composition by mass. Write and construct balanced equations. Perform calculations involving the mole concept, reacting masses, volumes of gases, and volumes and concentrations of solutions. Deduce stoichiometric relationships from calculations involving reacting masses, volumes of gases, and volumes and concentrations of solutions. Relative Atomic Mass and the Mole 🧮: Relative atomic mass is the weighted average mass of naturally occurring atoms of an element on a scale where an atom of carbon-12 has a mass of exactly 12 units. The mole is a unit used to count the number of particles in a substance and is based on the Avogadro constant. Empirical and Molecular Formulas 📝: Empirical formulas show the simplest whole-number ratio of atoms in a compound. Molecular formulas show the total number of atoms of each element present in one molecule or one formula unit of the compound. Balancing Chemical Equations ⚖️: Chemical equations must be balanced to ensure that the number of atoms of each element on the reactants side is equal to the number on the products side.

< Back IGCSE Cambridge Chemistry 0620 O level Chemistry For IGCSE Cambridge syllabus Go to Course Page Notes Questions and worksheets Previous Next

Insoluble ​ ​ The inability of a substance to dissolve in a particular solvent, resulting in a heterogeneous mixture.

The burning of a magnesium ribbon in air Grade 10 SABIS SABIS Exothermic

Physical properties of metals: shiny, ductile (pulled into wires), malleable (hammered into thin sheets), conduct electricity. Grade 10 SABIS ​

Reaction Mechanism: reactions rarely proceed in a single step as written. They take place in a series of smaller steps called a reaction mechanism. Grade 10 SABIS ​

Combustion Reactions Grade 10 SABIS SABIS Reaction when a substance reacts rapidly with a gas producing heat and light, for eg., burning a substance in the presence of air

Microscopic changes that take place when a liquid is warmed Grade 10 SABIS ​ When a liquid is warmed in thermochemistry, several microscopic changes occur at the molecular level. These changes involve the increased kinetic energy of the liquid molecules and their interactions, leading to observable macroscopic effects such as expansion and changes in physical properties. As the liquid is heated, the temperature of the system rises, and this increase in temperature corresponds to an increase in the average kinetic energy of the liquid molecules. The molecules gain energy and move more rapidly, exhibiting increased vibrational, rotational, and translational motion. The increased kinetic energy causes the intermolecular forces between the liquid molecules to weaken. In the liquid state, these forces, such as hydrogen bonding or London dispersion forces, hold the molecules together in a cohesive arrangement. As the molecules gain energy, the forces become less effective at maintaining this cohesion. The weakened intermolecular forces result in an expansion of the liquid. The increased molecular motion and reduced intermolecular forces allow the molecules to move farther apart, leading to an increase in volume. This expansion is commonly observed in liquids when they are heated. Additionally, the increased kinetic energy can lead to changes in the physical properties of the liquid. For example, the viscosity of the liquid may decrease as the molecules move more freely and with less resistance. The surface tension may also decrease as the cohesive forces weaken, affecting the behavior of the liquid at interfaces. Furthermore, in some cases, when a liquid is heated sufficiently, it may undergo a phase change and transform into a gas. This transition occurs at the boiling point, where the vapor pressure of the liquid becomes equal to the external pressure. The heated liquid absorbs energy to overcome intermolecular forces and transition into a gas phase. It's important to note that the microscopic changes in a liquid being warmed are reversible. When the liquid is cooled, the molecules lose kinetic energy, and the intermolecular forces regain their effectiveness, leading to a decrease in volume and a return to the initial state. Understanding the microscopic changes that occur when a liquid is warmed is crucial in thermochemistry and various applications. It allows us to analyze energy transfers, phase transitions, and the behavior of substances under different temperature conditions. In summary, when a liquid is warmed in thermochemistry, microscopic changes take place at the molecular level. The increased kinetic energy of the molecules weakens the intermolecular forces, resulting in expansion, changes in physical properties, and, in some cases, phase transitions. Recognizing and studying these microscopic changes enhances our understanding of energy transfer and the behavior of liquids at different temperatures.

Mathematical Representation ​ ​ P1V1 = P2V2, which signifies that the product of initial pressure and volume equals the product of final pressure and volume.

7. The decomposition of water into H2 and O2 gas. Endothermic Grade 10 SABIS SABIS