3.1.4 ENERGETICS, A LEVEL CHEMISTRY, AQA QUESTIONS AND ANSWERS WITH SOLUTIONS 2024 What is enthalpy change? - ANSWER Heat energy transferred in a reaction at constant pressure What are standard conditions for enthalpy change? - ANSWER 100kPa and stated temperature (normally 25 degrees celcius) What values of deltaH do exothermic reactions have? - ANSWER Negative (less than 0) What values of deltaH do endothermic reactions have? - ANSWER Positive (more than 0) What do exothermic reactions do with energy? - ANSWER Give out energy What do endothermic reactions do with energy? - ANSWER Absorb energy Are oxidation reactions endo or exothermic? - ANSWER Exothermic Is combustion endo or exothermic? - ANSWER Exothermic Are thermal decomposition reactions endo or exothermic? - ANSWER Endothermic Is photosynthesis endo or exothermic? - ANSWER Endothermic What happens to reactant bonds? - ANSWER They are broken What happens to product bonds? - ANSWER They are formed Which bonds are broken: reactant or product bonds? - ANSWER Reactant Which bonds are formed: reactant or product bonds? - ANSWER Product Is energy taken in or released when you break bonds? - ANSWER Taken in Is bond breaking endo or exothermic? - ANSWER Endothermic What values of deltaH does bond breaking have? - ANSWER Positive (more than 0) How does bond breaking energy change as the bond strength increases? - ANSWER It takes more energy to break Is energy taken in or released when you make bonds? - ANSWER Released Is bond making endo or exothermic? - ANSWER Exothermic What values of deltaH does bond making have? - ANSWER Negative (less than 0) How does bond making energy change as the bond strength increases? - ANSWER They release more energy when formed If you need more energy to break bonds than is released when bonds are made, what values of deltaH do you get? - ANSWER Positive (more than 0) If you need less energy to break bonds than is released when bonds are made, what values of deltaH do you get? - ANSWER Negative (less than 0) What is bond enthalpy? - ANSWER The energy required to break bonds
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