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5 use bond energies (ΔH positive, i.e. bond breaking) to calculate enthalpy change of reaction, ΔHr A Level Chemistry CIE Bond energies play a crucial role in calculating the enthalpy change of a chemical reaction (ΔHr). Bond energies represent the amount of energy required to break a particular bond within a molecule. By utilizing bond energies, we can estimate the overall energy change associated with the breaking and formation of bonds during a reaction. To calculate the enthalpy change of a reaction (ΔHr) using bond energies, we follow a simple approach. First, we identify the specific bonds that are broken and formed in the reaction. Then, we determine the bond energies for these bonds from reliable sources such as databases or experimental data. The bond energies typically have positive values, indicating that energy is required to break the bonds (ΔH positive, i.e., bond breaking). These bond energies are expressed in units of energy per mole (kJ/mol) and represent the average energy needed to break the bond in a large number of molecules. Next, we sum up the bond energies for the bonds broken in the reactants. This represents the energy required to break these bonds. We subtract the sum of the bond energies for the bonds formed in the products. This represents the energy released during the formation of new bonds. The enthalpy change of the reaction (ΔHr) can then be calculated as the difference between the total energy required to break the bonds and the total energy released during the formation of new bonds. The ΔHr value obtained from bond energies is an estimation of the enthalpy change, assuming the reaction occurs under standard conditions. It's important to note that bond energies are approximate values and can vary depending on the specific molecular environment and conditions. They provide a useful estimate for calculating enthalpy changes, but actual experimental values may differ due to factors such as bond strength variations and different reaction conditions. For example, in the combustion of methane (CH4) to form carbon dioxide (CO2) and water (H2O), we can use bond energies to estimate the enthalpy change. The C-H bonds in methane are broken, requiring energy input. At the same time, new bonds (C-O and O-H) are formed in the products, releasing energy. By summing up the bond energies for the broken and formed bonds, we can calculate an approximate enthalpy change for the reaction. Using bond energies to calculate the enthalpy change of a reaction provides a valuable tool for estimating energy changes in chemical processes. It allows us to gain insights into the energetics of reactions, compare the relative stabilities of different compounds, and predict the feasibility of chemical transformations. In summary, bond energies can be used to estimate the enthalpy change of a reaction (ΔHr) by summing up the energy required to break the bonds in the reactants and subtracting the energy released during the formation of new bonds in the products. Although bond energies provide approximate values, they serve as a useful tool for understanding the energy transformations involved in chemical reactions and making predictions about their enthalpy changes.

Atoms Grade 10 SABIS SABIS The smallest unit of an element that retains the chemical properties of that element.

Know the Potential Energy diagram for an Exothermic and Endothermic reactions Grade 10 SABIS ​ To understand how to determine the potential energy diagram for exothermic and endothermic reactions, let's first discuss what a potential energy diagram represents. A potential energy diagram is a graphical representation that shows the changes in potential energy of a chemical system as a reaction progresses. The vertical axis of the diagram represents the potential energy, while the horizontal axis represents the progress of the reaction from the initial state to the final state. Now, let's focus on exothermic reactions. An exothermic reaction is one that releases energy to the surroundings, usually in the form of heat. In an exothermic reaction, the products have lower potential energy than the reactants. This means that the potential energy decreases as the reaction proceeds. On a potential energy diagram for an exothermic reaction, the reactants are represented at a higher energy level compared to the products. The curve starts at a higher point (representing the energy of the reactants) and gradually decreases (representing the decrease in potential energy) as the reaction progresses towards the products. The difference in potential energy between the reactants and products is the amount of energy released to the surroundings. Now, let's move on to endothermic reactions. An endothermic reaction is one that absorbs energy from the surroundings. In an endothermic reaction, the products have higher potential energy than the reactants. This means that the potential energy increases as the reaction proceeds. On a potential energy diagram for an endothermic reaction, the reactants are represented at a lower energy level compared to the products. The curve starts at a lower point (representing the energy of the reactants) and gradually increases (representing the increase in potential energy) as the reaction progresses towards the products. The difference in potential energy between the reactants and products is the amount of energy absorbed from the surroundings. To determine the shape of the potential energy diagram, it is essential to consider the activation energy, which represents the energy barrier that must be overcome for the reaction to occur. The activation energy is depicted as the peak on the potential energy diagram. For an exothermic reaction, the activation energy is usually lower than the potential energy of the reactants, indicating that the reaction can readily occur. The potential energy decreases from the reactants to the products, with the activation energy acting as the barrier that needs to be overcome. In contrast, for an endothermic reaction, the activation energy is typically higher than the potential energy of the reactants. This indicates that more energy is required for the reaction to proceed. The potential energy increases from the reactants to the products, with the activation energy representing the energy threshold that must be surpassed. In summary, the potential energy diagram for exothermic reactions shows a gradual decrease in potential energy from the reactants to the products, while the diagram for endothermic reactions shows a gradual increase in potential energy. The activation energy represents the energy barrier that must be overcome. Understanding these diagrams helps visualize the energy changes and barriers involved in the progress of chemical reactions.

General physical properties of non-metals: brittle, do not have a luster do not conduct heat or electricity Grade 10 SABIS ​

Dissolving salt into water to make a solution Grade 10 SABIS SABIS Physical

Coefficients Grade 10 SABIS SABIS The numbers placed before the reactants and products in a chemical equation, indicating how many molecules or atoms are involved.

Recognize an endothermic/exothermic process, basing on knowledge and lab experience Grade 10 SABIS ​ Endothermic Processes: Melting ice or any solid substance. Evaporation of water or any liquid. Photosynthesis in plants, where sunlight is converted into chemical energy. Dissolving ammonium nitrate in water. Decomposition of limestone into lime and carbon dioxide upon heating. Electrolysis of water to produce hydrogen and oxygen gas. Absorption of heat by a cold pack to provide a cooling effect. Cooking food in an oven, where heat is absorbed by the food. The process of converting liquid water into steam. Dissolving barium hydroxide octahydrate in water. Exothermic Processes: Combustion of wood or any fuel, releasing heat and light. Formation of rust (oxidation of iron) with the release of heat. Neutralization of an acid with a base, such as hydrochloric acid and sodium hydroxide. Respiration in living organisms, where energy is released from glucose. Reaction between vinegar (acetic acid) and baking soda (sodium bicarbonate), resulting in the release of carbon dioxide gas. Reaction between sodium and chlorine to form sodium chloride, releasing heat and light. Freezing of water, where heat is released to the surroundings. Exothermic polymerization reactions, such as the curing of epoxy resin. Formation of precipitates during double displacement reactions, accompanied by the release of energy. Formation of bonds in exothermic chemical reactions, such as the reaction between hydrogen and oxygen to form water.

Standard Temperature and Pressure (STP) Grade 10 SABIS SABIS 0⁰C and 1.00 atm pressure

Reaction of Alkali metals with oxygen. Grade 10 SABIS ​ Generally: 4M(s) + O2(g) → 2M2O(s) alkali metal + oxygen → alkali metal oxide

Convenient Reaction Ratio Grade 10 SABIS SABIS The ratio in which reactants combine or react to form products. It is often based on the coefficients in the balanced chemical equation and is used to simplify stoichiometric calculations.

< Back Electrochemistry ​ ​ Previous Next 🔬 Chapter 7: Redox Reactions 🔬 Learning Outcomes 🎯: Calculate oxidation numbers of elements in compounds and ions. Describe and explain redox processes in terms of electron transfer and changes in oxidation number. Use changes in oxidation numbers to help balance chemical equations. What is a Redox Reaction? 🔄: Oxidation is the gain of oxygen by an element or the loss of electrons. Reduction is the loss of oxygen or the gain of electrons. Redox reactions involve both oxidation and reduction processes. Oxidation and reduction always take place together in redox reactions. Redox reactions are crucial in various natural processes such as photosynthesis and respiration. Oxidation Numbers and Electron Transfer ⚖️: Oxidation numbers can be used to determine whether a substance has been oxidized or reduced during a chemical reaction. An increase in oxidation number indicates oxidation, while a decrease indicates reduction. Redox reactions can also be explained in terms of electron loss (oxidation) or electron gain (reduction). Balancing Redox Reactions 🧮: Half-equations can be used to represent the oxidation and reduction processes separately. Balancing redox reactions involves ensuring that the number of electrons lost in the oxidation process is equal to the number of electrons gained in the reduction process. Examples of Redox Reactions 🧪: The reaction between magnesium and oxygen to form magnesium oxide is an example of a redox reaction. The reaction between sodium and chlorine to form sodium chloride involves the transfer of electrons and is also a redox reaction. Rusting is an oxidation reaction that involves the reaction of iron with oxygen in the presence of water.

cm³ Grade 10 SABIS SABIS A unit of volume equal to one cubic centimeter, equivalent to 1 milliliter.