Changes all around us Flashcards
What is a chemical change? When does a chemical change occur
A chemical change also called a chemical reaction occurs when matter changes into a brand new substance with different properties.
Example: Burning of methane. Methane is the main component of natural gas, when burnt it combines with the oxygen in the air and changes into the gasses CO2 and water vapour.
What are reactants and products?
Reactants are the substances that react with one and another while products are the substance made from the reactants.
How to identify a chemical change?
The evidence of a chemical change is:
- Release of bubbles
- A change of colour
- A new substance is formed
- Odor is produced
- Change in temperature
- Noise is given off
Can a chemical change be undone?
A chemical change cannot usually be reversed as the matter changes with new properties. But in some cases, a chemical change can be undone, but with another chemical change to reverse it.
What is the law of conservation of mass?
The law of conservation of mass states that matter cannot be created nor destroyed. The matter, whether it goes through a physical or chemical change will have the same mass as it had before the change.
How do bonds change in a chemical reaction?
The reactants and products in a chemical change contain the same atoms but the atoms are rearranged during the reaction. This happens because chemical bonds creak in the reactants and the new chemical bonds form in the products.
What are the types of chemical reactions?
Type of Reaction General Equation Example
Synthesis = A+B → C = 2Na + Cl2 → 2NaCl
Decomposition = AB → A + B = 2H2O →2H2 + O2
Single Replacement = A+BC → B+ AC 2K + 2H2O →
2KOH + H2
Double Replacement = AB+ CD → AD + CB = NaCl+ AgF → NaF + AgCl
Combustion = fuel + oxygen → carbon dioxide + water = CH4 + 2O2 → CO2 + 2H2O
What are endothermic and exothermic reactions?
Endothermic - More energy is released when bonds form in products that are used to break bonds in reactants. These Reactions absorb energy from the environment.
Exothermic - More energy is released when bonds form in products and then is used to break bonds in reactants. These reactions release energy to the environment, often in the form of heat or light.
What are irreversible reactions?
Irreversible reactions are reactions that can not be reversed once done. The reactants can change to products but products can’t change to reactants. Cumbustion is usually an irreversible reaction. The fuel and oxygen can turn into CO2 and water vapour but the CO2 and water vapour can’t change back to fuel and oxygen
What are reversible reactions?
Reversible reactions are reactions that can move both ways. Reactants become products and products become reactants. The product can change back to the reactant under certain conditions through another chemical change.
What is the balancing act?
In a reversible reaction, both forward and reverse reactions occur at the same time. While reactants are reacting to produce products, products are reacting to produce reactants. Often, a point is reached at which forward and reverse directions of the reaction occur at the same rate. When this happens, there is no overall change in the number of reactants and products. This point is called equilibrium (State of balance).
Balancing chemical equations
To balance a chemical equation there must be the same number of each type of atom on both sides. The general form of a chemical reaction is to form from a reactant to a product. When balancing equations we can’t change the subscript but we can change one of the coefficients. Chemicals reactions must be balances as mass is always conserved in a chemical reaction.
