Question

Chemical Change and Chemical Equations Name G No. Pre-lab Questions: Classify each of the following changes as physical or chemical and, in the cases of a chemical change, describe one observation that indicates new substances have been formed 1. a. Milk sours b. A wet handkerchief dries c. Fruit ripens d. A stick of Dynamite explodes Air is compressed into a steel container f. Water boils g. A baking cake burns h. A silver tray tarnishes i. On a hot day, drops of water collect on the outside of a glass holding iced e. tea 2. Define the following terms: a) Exothermic reaction b) Endothermic reaction 3. You will perfrom the following reaction in the lab. i. Which substances or compounds are reactants? ii. Which substances or compounds are products? [continue

Answer 1

1)

a)

Milk Sours

It is a chemical change, there is composition of milk changes.In this reaction milk is completely change to yogurt by bacterial fermentation reaction.

b)

A wet handkercheif dries

It is a physical change, since there is only water is evapourated and leaves the kercheif dry.

c)

Fruit ripens

It is also a chemical change in which due to bacterial fermentation friut ripens and change the colour.

d)

A stick of dynamite explodes

Dynamite is a composition of explosive materials so when it explodes then there is a change in the composition of chemical and produce ash products with high enegy so it is a chemical change

e)

Air composed into a steel container

It is a physical change since we associate the air particles closed each other if we release the pressure then air will get normal state

f)

water boils

It is a physical change since water change its state from liquid to gas state by giving heat energy if the energy released then the water will be formed.

g)

A baking Cake burns

It is a chemical changes since after baking the raw material to cake it cannot be get to it's initial state.

h)

A silver tray tarnishe

It is a chemical change since the silver metal under go oxidation with O2 present in the air and tarnished and cannot give its initial state

i)

On a hot day, drops of water collect on the outside of a glass holding iced tea

It is a phical change since only heat is transferd with respect to temperature.

2)

a)

Exothermic reaction:

In a reaction the heat energy is released along the products then the reaction is called as exothermic reaction.

Endothermic reaction:

In a reaction the heat enery is required for reactants to get the products is called as endothermic reaction.

3)

Mg(s) + 2 HCl(aq) -----> MgCl2(aq) + H2(g)

Mg and HCl are the reactants

MgCl2 and H2 are the products

2Al(s) + 6 HCl(aq) ------> 2AlCl3(aq) + 3H2(g)