4. For a reaction to occur, energy must be_

__ to break chemical bonds.

A collection of coins contains 15 pennies, 12 dimes, and 7 quarters. What is the percentage of pennies in the collection? Express your answer to two significant figures and include the appropriate units.

Uma indústria de confecção de placas de alumínio deseja transportar 100 placas de alumínio para um cliente. Considerando que o veículo de transporte pode carregar até 3 toneladas e que a dimensão de cada placa são 2 M X 50 Cm X 2cm Calcule,

Give an example of a system in which people use steam for a mechanical advantage.

The fe (ox33 - complex ion creates an emerald green solution when dissolved. the observed solution color of the complex indicates the size of δ o is:

A reaction of 12.640 g of copper oxide with 0.316 g hydrogen produces 2.844 g of water and Xg of copper. X=_9

What is the significance of the symbol of an element?

Consider the half reactions below for a chemical reaction. 2 Equations: First: upper M g right arrow upper M g superscript 2 plus (a q) plus 2 e superscript minus.

If you put some sodium chloride (table salt) into a glass of water, what will happen?

Why don't the inert gases easily react with other elements?

What is the name of the following compound Pb (CH3COO) 4