Chemical and physical changes
How do chemical reactions occur?
How can the reaction rate be increased?
Ajuste de ecuaciones químicas
Ley de conservación de la masa y ley de las proporciones definidas
Stoichiometric calculations
100
True or false:
In a chemical change, there is a change in the composition of the substances.
True.
100
The theory that explains how chemical reactions occur is called....
Collision theory.
100
List two factors that can increase the rate of a reaction.
-Temperature
-Reactant contact area
-Reactants concentration
-The presence of catalysts
100
Why do you have to balance a chemical equation? How do you do this process?
Para igualar el número de átomos de cada elemento en los reactivos y en los productos, añadiendo para ello coeficientes estequiométricos.
100
Is the law of conservation of mass fulfilled in the following experiment? Explain your answer.
Zn+ HCl → ZnCl2+ H2
65g+73g→ 136g+ 2g
Sí se cumple, ya que la masa de los reactivos es igual a la masa de los productos.
100
Balance the chemical equation and indicate the proportion in moles provided by it:
Zn + CuSO4 → Cu + ZnSO4
Zn + CuSO4 → Cu + ZnSO4
1mole + 1mole 1mole + 1mole
200
Is it a chemical or a physical change?
Physical change.
200
True or false (correct the sentence in case it is false):
According to the theory that explains how chemical reactions occur, it doesn't matter the orientation of the reactants molecules when they collide, products will always be formed as a result of the collision.
False, the reactants must collide with the proper orientation.
200
Marble reacts with hydrochloric acid. If I have a piece of marble and I'm going to mix it with a hydrochloric acid solution, what can I do to increase the rate of this reaction?
Disminuir el tamaño del mármol para aumentar la superficie de contacto y que así se de un mayor número de choques entre los reactivos, por ejemplo machacándolo.
200
What are the reactants, products and stoichiometric coefficients in this reaction:
N2 + 3 H2 → 2 NH3
Stoichiometric coefficients: 1, 3 y 2.
Reactants: N2, H2
Product: NH3
200
What is the mass of dichloride? What law are you using?
Na + Cl2 → NaCl
46g+ ? → 117g
mass Cl2= 71 g
200
Balance the next chemical equation:
HCl + Ca(OH)2 → CaCl2+ H2O
How many moles of CaCl2 will be produced when 0,84 moles of HCl react?
2HCl + Ca(OH)2 → CaCl2+ 2H2O
0,84mole 0,42 mole
300
Is it a chemical or a physical change?
Chemical change.
300
In order for the collisions to be effective, what are the two conditions that must be met simultaneously?
-Proper orientation of the reactants.
-The reactants particles must have enough energy to break the bonds between the atoms.
300
True or false:
Catalysts are substances that increase of decrease the rate of chemical reactions but aren't changed or consumed during the process.
True.
300
True or false:
The molecular representation of the reaction match the chemical equation. Explain your answer.
Falso. En el ajuste de la ecuación química falta un 2 delante del oxígeno molecular.
300
According to the proportions given for the next reaction, find out the mass of nitrogen that will react with 12 grams of hydrogen.
What law are you using?
N2 + H2 → NH3
28g+ 6g
? +12g
(28g N2)/(6g H2)=(xg N2)/(12g H2)
56g N2
300
diiron trioxide reacts with carbon monoxide, producing carbon dioxide and metallic iron.
a)Write down and balance the chemical equation of this process.
b) How many moles of diiron trioxide are needed to produce 1,95 moles of iron?
a) Fe2O3 + 3CO → 3CO2+ 2Fe
b) 0,975 moles of Fe
400
Is it a chemical or a physical change?
Melting a metal: Physical change.
400
Explain how the molecules of the products are formed according to the theory mentioned before.
Los átomos de los reactivos se separan al chocar de forma eficaz y se unen de formas diferentes dando los productos.
400
Copper(II) sulfate reacts with metallic zinc. Which of these process will be faster? Why?
a) If we prepare a copper(II) sulfate solution with a concentration of 5% by mass and introduce a piece of zinc.
b) If we prepare a copper(II) sulfate solution with a concentration of 10% by mass and introduce a piece of zinc.
La b), puesto que la concentración es el doble, luego habrá más sulfato de cobre (II), se producirán más choques y la reacción será más rápida.
400
Balance the next chemical equation:
Fe2O3 + CO → Fe + CO2
Fe2O3 + 3 CO →3 Fe + 2 CO2
400
What would be the masses of ammonia produced in the process showed in last question?
a) 34 g NH3
b) 68 g NH3
400
In the decomposition of hydrogen peroxide (H2O2), hydrogen gas and oxygen gas are produced.
a) Write down and balance the chemical equation.
b) If 50 grams of hydrogen peroxide react, how many moles of hydrogen gas will be produced?
a) H2O2 → H2 + O2
b) MH2O2=2*1g/mol+2*16g/mol=34g/mol
50g H2O2=1,47 moles H2O2
1,47 moles H2
500
Is it a chemical or a physical change?
Chemical change.
500
Choose the correct answer.
What doesn't change in a chemical reaction?
a) Number of molecules
b) Substances
c) The atoms
d) The number of moles
c) The atoms
500
Explain why the higher the temperature of the medium where a chemical reaction takes place, the faster it will be.
Use kinetic-molecular theory to help you do this.
A mayor temperatura, mayor velocidad y energía de las moléculas de los reactivos, se producen más choques y son más energéticos, luego es más fácil que estos choques sean eficaces, dando como resultado la formación de productos.
500
Balance the next chemical equation:
HCl+ Al2O3 → AlCl3+ H2O
6HCl+ Al2O3 → 2AlCl3+ 3H2O
500
Find out the amount of carbon dioxide. Explain the law you are using.
CH4 + 2 O2 → CO2 + 2 H2O
16g + 64 g→ ? + 36 g
44 g de CO2
Ley de conservación de la masa: En una reacción química, la masa se conserva, siendo la masa de los reactivos igual que la masa de los productos.
500
a) Write down and balance the chemical equation of the combustion of propane (C3H8).
b) If 420 kg of propane combust, what is the mass of water vapor produced?
a) C3H8 + 5O2 → 3CO2 + 4H2O
b) MC3H8=3*12g/mol+8*1g/mol=44 g/mol
420 kg C3H8= 4,2*105 g C3H8
9545,45 mol C3H8
38181,81 mol H2O
687272,73 g H2O= 6,873 kg H2O