Review energy changes by identifying the correct statements about each reaction.

2H2(g) + O2(g) ---> 2H2O(l) + 136.6 kcal

ANSWERS:
The reaction is: exothermic

The delta H value is: negative

Heat is a: product

The reaction is exothermic

The value is negative.

Heat is a product.

Explanation:

Endothermic reactions are defined as the reactions in which energy of the product is greater than the energy of the reactants. The total energy is absorbed in the form of heat and for the reaction comes out to be positive.

Exothermic reactions are defined as the reactions in which energy of the product is lesser than the energy of the reactants. The total energy is released in the form of heat and for the reaction comes out to be negative.

The substances which are written on the left side of the arrow are reactants and the substances which are written on the right side of the arrow are products. Thus heat is a product.

We can observe physical properties of elements and compounds without changing the substance.

Examples of physical properties: Density, color, boiling point, state of matter, appearance: dull or shiny, etc. 

But we can also observe and measure chemical properties by reacting a substance with something else. For example, like mixing baking soda and vinegar together. The vinegar reacts with the baking soda and produces carbon dioxide: a new substance. 

Some examples of chemical properties: Flammability, amount of heat that is released during combustion, toxicity (how much damage it causes to other organisms), radioactivity, and ability to oxidize (when you have metal that becomes rusty looking).