Chemistry - 2nd sem Flashcards
What is the law of conservation of mass?
Mass can neither be created nor destroyed.
Define an exothermic reaction.
When reactants transform into products, they release energy as they form bonds, and therefore lose their potential energy, as the surroundings increase in temperature.
Define an endothermic reaction.
When reactants transform into products, they absorb energy in order to break bonds, and therefore gain potential energy, and the surroundings decrease in temperature.
A lot of reactions involve both the breakage and formation of bonds. What tells us if it is endothermic, or exothermic - not being able to measure the temperature.
A reaction would be endothermic when the energy released from making bonds is much greater than the energy absorbed in order to break the reactant bonds in order to form the product bonds. This happens when the bonds holding together the reactants aren’t very strong and not much energy is required in order to break these. The same is said in an opposite manner for endothermic reactions.
Why is it that energy is released when bonds are formed?
It takes a lot of energy in order to form bonds, and so the molecules use whatever energy they already have in order to form bonds, that by when they’ve done so, they’ve exhausted and used up a lot of their energy - which is released in the process to the surroundings as heat.
Why is it that energy is absorbed in order to break bonds?
Energy is absorbed to break bonds
What is a decomposition reaction?
In a decomposition reaction, one compound breaks down into two or more substances.
E.g. lead nitrate —-(heating)—–> lead oxide + nitrogen dioxide + oxygen
What is a combination reaction?
A combination reaction is a reaction in which two or more elements or compounds combine together to form a single compound.
E.g. magnesium + oxygen —–(heating)—-> magnesium oxide
What is a reaction rate?
How quickly reactants are consumed or products are made.
How does temperature affect the reaction rate?
Higher temperatures allow for higher reaction rates because:
- The particles have more energy and move quickly therefore more collisions and so they breakdown the CaCO3 more quickly.
- Activation energy - in order for a reaction to occur, the reactants have to have a certain amount of energy; if the temperature is higher that means the particles have more energy, they have on average, energy above the activation energy and are thus more likely to react.
What is a mol?
A mol is a unit of measurement, specifically 6.02 x 10^23 atoms/molecules.
What is a combustion reaction?
An exothermic reaction involving an alcohol and an oxidant (usually oxygen) producing water, carbon dioxide, and heat.
What is a precipitation reaction?
A reaction involving two soluble salts reaction to produce an insoluble salt.
