IG Chemistry-7 Chemical energetics (7.1/7.2)

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What is an exothermic reaction?

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An exothermic reaction is a chemical reaction that releases heat energy to the surroundings, resulting in an increase in temperature of the surroundings.

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What is an endothermic reaction?

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An endothermic reaction is a chemical reaction that absorbs heat energy from the surroundings, resulting in a decrease in temperature of the surroundings.

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What is the enthalpy change (ΔH) in a chemical reaction?

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The enthalpy change (ΔH) is the heat content change of a system at constant pressure, indicating whether a reaction is exothermic (negative ΔH) or endothermic (positive ΔH).

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What happens to energy during combustion reactions?

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During combustion reactions, energy is released in the form of heat and light, making them exothermic.

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What is the significance of the negative sign in ΔH = -572 kJ/mol for the combustion of hydrogen?

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The negative sign indicates that the reaction releases 572 kJ of energy per mole of hydrogen burned, confirming it is an exothermic reaction.

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How do you calculate the total energy released in a reaction?

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To calculate the total energy released, multiply the enthalpy change (ΔH) by the number of moles of reactant used.

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What is a physical change?

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A physical change is a change that affects one or more physical properties of a substance without altering its chemical composition.

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Give an example of a chemical change.

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Rust forming on nails is an example of a chemical change, as new substances are formed and energy is released.

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What is the difference between a physical change and a chemical change?

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A physical change alters the form or appearance of a substance without changing its composition, while a chemical change results in the formation of new substances.

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What is the role of activation energy in chemical reactions?

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Activation energy is the minimum energy required for reactants to collide and form products in a chemical reaction.