Is the reaction when a candle is burning Exothermic or endothermic? Explain
Exothermic Heat is released when the candle (wax) burns.
When the candle was lit, a pool of liquid wax formed in the area around the wick, and then spilled over the side and re solidified. Does this observation refer to a physical or a chemical change? Explain
A physical change. The substance was still wax, but it changed to a liquid and then back to a solid.
Carbon, hydrogen, and oxygen. No matter is created or destroyed in a chemical reactions, and so the elements present in the products must have been present in the reactants.
The flame of a burning candle gives off black smoke. Does this statement describe evidence for a physical change or a chemical change? Explain.
A chemical change. The black smoke is evidence of the formation of a new substance, which means a chemical change occurred.
Is a burning candle an example of an open of closed system? explain
An open System. In an open system, matter can enter from or escape to the surroundings. IN a closed system, matter is not allowed to enter or leave. When a candle burns, oxygen is allowed to enter and smoke is allowed to leave, so it is an open system.
For the following reaction tell whether it is exothermic or endothermic. Explain your reasoning in terms of the energy of the reactants and products. A log burns in the fireplace giving off gases and ash.
The reaction is exothermic because heat and light are given off. The energy of the products is less that the energy of the reactants.
For the following reaction tell whether it is exothermic or endothermic. Explain your reasoning in terms of the energy of the reactants and products. When vinegar and baking soda are mixed, new substances form and the solution becomes cooler.
The reaction is endothermic. Energy is absorbed by the reaction, making the solution feel cooler. The energy of the products is greater than the energy of the reactants.
Compare a physical change and a chemical change.
A physical change is a change only in the form or appearance of a substance; the substance does not change into any other substances. A chemical change occurs when elements and compounds combine in different ways, producing one or more substances that were not present before.
Relate the writing and balancing of a chemical equation to the principle of conservation of mass.
The principle of conservation of mass states that matter cannot be created or destroyed during a chemical reaction. Therefore, the number and kind of atoms going into a chemical reaction must exactly equal the number and kind of atoms coming out of the reactions. A balanced chemical equation must show that all the elements present in equal amounts in the products.
Explain which bonds are broken and which bonds are formed during the reaction of magnesium and oxygen to form magnesium oxide. Identify which substances are compounds and which are elements. 2 Mg + O 2 --> 2 MgO
The bonds between oxygen atoms in O 2 are broken. Bonds form between magnesium and oxygen in MgO. Mg and O 2 are elements, and MgO is a compound.
Describe the difference between a synthesis reaction and a decomposition.
A synthesis reaction produces a more complex substance from a simpler substances. A decomposition reaction produces simpler substances from a more complex substance. These two reactions are opposite processes.
How many atoms are in the following chemical formulas? A.Ba 3 P 2 B.Ba(OH) 2 C.NH 4 Br D.Ca 3 (PO 4 ) 2 E.K 2 SO 3