What is the difference between firewall and ACL?

ACL is not a mahanism it is just permission and ACL do not know that what comes before means if any ACk of TCP comes on the ACL then it's just react as the policy,where as firewall checks all the result of ACK and knows the conversation of TCP from beginning.

IN ACL if you are making a policy of any port basis then ACL always have open gate for the same either it is working or not but firewall open the gate at that time when the we require the policy.