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| Questão | Responda |
| What is enthalpy change? | Enthalpy change (ΔH) is the heat energy transferred in a reaction at constant pressure. The units of ΔH are kJmol⁻¹ |
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It shows that the measurements were made under standard conditions and that the elements were in their standard states |
| What are the standard conditions? | 100kPa (about 1 atm) pressure 298K (25°C) temperature |
| You can't directly measure the actual enthalpy of a system. What is used instead? | Enthalpy change - you can find these either by experiment or in data books |
| Complete the sentences: Enthalpy changes in data books are usually _____________ enthalpy changes. This is important as changes in enthalpy are affected by ______________ and ____________. | Enthalpy changes in data books are usually STANDARD enthalpy changes. This is important as changes in enthalpy are affected by PRESSURE and TEMPERATURE. |
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Standard enthalpy change of reaction |
| Define standard enthalpy change of reaction | The enthalpy change when a reaction occurs in the molar quantities shown in the chemical equation, under standard conditions with all reactants and products in their standard states |
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Standard enthalpy change of formation |
| Define standard enthalpy change of formation | The enthalpy change when 1 mole of a compound is formed from its elements in their standard states under standard conditions |
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Standard enthalpy change of combustion |
| Define standard enthalpy change of combustion | The enthalpy change when 1 mole of a substance is completely burned in oxygen under standard conditions with all reactants and products in their standard states |
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Standard enthalpy change of neutralisation |
| Define standard enthalpy change of neutralisation | The enthalpy change when solutions of an acid and an alkali react together to form 1 mole of water, under standard conditions |
| Complete the sentences: Exothermic reactions _______ ______ energy to their surroundings. The products of the reaction end up with _______ energy than the reactants. This means that the enthalpy change for the reaction will be ___________. | Exothermic reactions GIVE OUT energy to their surroundings. The products of the reaction end up with LESS energy than the reactants. This means that the enthalpy change for the reaction will be NEGATIVE. |
| TRUE OR FALSE: Oxidation is usually exothermic | TRUE |
| Describe what an enthalpy diagram of an exothermic reaction looks like |
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| Complete the sentences: Endothermic reactions ______ ____ energy from their surroundings. This means that the products of the reaction have ______ energy than the reactants, so the enthalpy change for the reaction is ___________. | Endothermic reactions TAKE IN energy from their surroundings. This means that the products of the reaction have MORE energy than the reactants, so the enthalpy change for the reaction is POSITIVE. |
| TRUE OR FALSE: Thermal decomposition is endothermic | TRUE |
| Describe what an enthalpy diagram of an endothermic reaction looks like |
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