Exothermic, Endothermic reactions and Energy Transfer Flashcards
What is an exothermic reaction?
A reaction in which energy is transferred from the reacting substances to their surroundings
What is an endothermic reaction?
A reaction in which energy is transferred to the reacting substances from their surroundings
What always happens to energy in chemical reactions?
Energy is conserved
Two examples of exothermic reactions
Combustion (e.g., burning fuels like methane).
Neutralisation (e.g., acid + alkali reactions).
Two examples of endothermic reactions
Thermal decomposition (e.g., breaking down calcium carbonate into calcium oxide and carbon dioxide).
Photosynthesis (requires energy from sunlight).
What are the steps to investigate temperature change in a reaction using a polystyrene cup and a thermometer?
Measure initial temperature:
Use a thermometer to measure and record the starting temperature of the reactant placed into the polystyrene cup(e.g., an acid or alkali).
Add the second reactant:
Add the second reactant (e.g., alkali or solid) to the cup and quickly cover it with a lid, if available, to minimize heat loss.
Stir gently:
Stir the mixture carefully to ensure the reaction occurs evenly.
Measure temperature change:
Use the thermometer to record the highest or lowest temperature reached during the reaction.
Repeat for accuracy:
Repeat the experiment at least 3 times to calculate a reliable average temperature change.
Analyze results:
Calculate the temperature change by subtracting the initial temperature from the final temperature.
Explain the reaction that happens in a single-use handwarmer
The handwarmer uses the exothermic oxidation of iron. Iron turns to hydrated iron III oxide with sodium chloride as a catalyst.
Explain the reaction of a self-heating food container
The exothermic reaction of calcium oxide + water -> calcium hydroxide when a button is pressed at the bottom of a can that breaks a barrier and allows the calcium oxide and water to mix. However this takes up a lot of space in the can and takes a lot of time to heat the food or drink.
Explain the reaction in an immediate-use cooling pack
The endothermic reaction of ammonium nitrate kept separately in a cool pack from water in there too. When squeezed, the bag containing ammonium nitrate breaks allowing them to mix. When dissolving, the reaction takes in heat from it’s surroundings.
Explain the reaction that happens in a reusable handwarmer
A reusable handwarmer uses sodium ethanoate to form crystals after it has been dissolved in hot water and left to cool. The metal disc inside is clicked to scrape off some metal and start the crystallisation process.
Explain the trend of exothermic reaction on a reaction profile.
The reactants have more energy than the products. Over the progress of reaction, energy is released (exothermic) . The difference in energy between reactants and products is measured in KJ/mol.
Explain the trend of endothermic reaction on a reaction profile.
The reactants have less energy than the products. Over the progress of reaction, energy is taken in (endothermic) and the surroundings get colder. The difference in energy between reactants and products is measured in KJ/mol.
What is activation energy?
The minimum amount of energy needed before colliding particles of reactants have enough energy to make a reaction. On a reaction profile, the activation energy is the point of highest energy between reactants and products ( in the middle because allows reactants to form it’s products).
What are the energy trends of breaking and making chemical bonds in chemical reactions?
Breaking bonds absorbs energy (endothermic), Forming bonds releases energy (exothermic). It takes more energy to break a bond than to make one.
Why Breaking Bonds Is Endothermic
Breaking bonds requires energy to overcome the attraction between atoms. This energy input is necessary to separate the atoms, making the process endothermic.
